eBay Integration
Improvements
Several Custom Values for one Item Specific
In the latest version of M2E Pro there is an ability to add several Custom Values for one Item Specific in case this Specific supports multiple values.
The number of values depends on number of available values for particular Item Specific.
Amazon Integration
Added
Gift Wrap and Gift Message
In new version ability to specify settings for Gift Wrap and Gift Message was added. They are available in Gift Settings block in Selling Settings of the Amazon Listings.
These options influence just on Item offer level.
If you want it to be applied to your Items, you should make sure that these options are enabled in Global Account Settings in Seller Central.
Note: after upgrade Gift Wrap and Gift Message options will be disabled by default. So if for Amazon Items managed by M2E Pro you enabled these options directly in Seller Central, they will become disabled after the first Revise. To prevent this situation, please, check your settings and enable this options.
Recommendations for Suppressed Items
If there are any recommendations suggested to Product Information, they will be displayed as a warning icon in a SKU column of Listing grid.
To add or edit Product Information according to recommendations you can use Listing Settings and the setting of assigned Description Policy.
Fixes
"Handling Time" and "Restock Date" issue
Due to Amazon API changes in previous versions of M2E Pro occurs an issue with unexpected disabling of Handling Time and Restock Date options. So without any changes in M2E Pro they used to be changed back to default values on Amazon.
It is fixed in new version and works properly now.
Constant revising of Items with Sale Price enabled
In previous versions there was an issue with Sale Price settings for Amazon Item. In case it was specified to take Sale Price value from Special Price of Magento Product, but the value of Special Price From date or Special Price To date was not provided, M2E Pro run Revise action for Price with each change.
It was not critical, but it was fixed in new version to improve M2E Pro Performance.
Rakuten.com Integration
Fixes
Some Major issues of New SKU Policy
In previous versions there were several issues with New SKU Policy. Now they are fixed and it is working correctly.
Play.com Integration
Removed
Integration no longer available
Play.com Integration was removed from current version of M2E Pro.
Play.com Marketplace was closed as a web-resource. It is connected with it’s removal and rebranding in Rakuten.co.uk.
M2E Pro stops support of Play.com Integration as technically Play.com and Rakuten.co.uk are totally different and it is necessary to create new ingration with Rakuten.co.uk.
M2E Pro is planning to release Rakuten.co.uk Integration at the end of 2015 beggining 2016 year.
Common Changes
Added
Catching changes of Magento Product Attributes
In current version M2E Pro extension can catch changes that were made using Update Attributes option in Catalog>Manage Products, that was not available earlier. 
Thus such Updates of Magento Products cause the same actions (List/Revise/Relist/Stop) as common products changes (Catalog>Manage Products>[selected product]>[change]>Save).
Price Deviation feature of Synchronization Policy
Conditional Revise for Price changes was added in new version of M2E Pro.
When this option is enabled, there is an ability to specify percent value of maximum possible Deviation between Magento Price (Selling Format Policy settings) and Item Price on the Channel, that can be ignored.
So how it works? If Magento Price is changed insignificantly (for several cents), the Revise will be run. It is absolutely normal, expected situation. However, when Price changes for all Magento Products (for example, due to currency rate changes), M2E Pro has to Revise all Items. It is resource and time-consuming, but usually there is no practical sense to update minimum Price changes. So if Conditional Revise option will be enabled, minimum changes will be ignored and M2E Pro will not spend a time to update them (e.g. from 23.47$ to 23.48$).
If Conditional Revise option is disabled, M2E Pro will update Price (that most likely has no practical effect). While Price Revise will be running for that Product, all changes (e.g. from 1$ to 60$ etc.) for other Products will be placed in queue and will wait until Price will not be updated. It can also increase the passivity of Orders Import up to 12 hours.
If this option is enabled and "Revise When Deviation More than" set to 3%, M2E Pro will ignore all changed in Magento Price that are lower than maximum Deviation value. So Price will not be Revised until it’s change will not be more or equal to Deviation value.
For example, Price is changed from 23.47$ to 23.48$. As Deviation Value (0.7$) is more than Price change (0.01$), Revise will not be run.
If Price is changed to 25$, Revise will be run, as Deviation Value (0.7$) is less than Price change (1.13$).
After Revise, for further Deviation count new Magento Price (25$) will be taken.
You can always change "Revise When Deviation More than" value according to your needs. The more value = less unusefull calls + more Performance of M2E Pro.
So M2E Pro does not recommend to disable this option.
Note: For Sellers who synchronize Magento Inventory with Suppliers Inventory by any automatic software this option is critically required, as Supplier's Price Values are changed very often.
Programmatic Possibilities to work with Extension
In new version of M2E Pro several PHP Classes were added. Using these Classes it is possible to notify Extension about Magento Products changes in different ways. This option is useful in case you are using a principle of direct SQL requests to update your Magento Products or any similar principle.
This programmatic components you can find following the next way \app\code\community\Ess\M2ePro\Model\PublicServices. The example of its possible usage is placed in a header of each code file.
More detailed information you can find here.
Plugin for Magmi Import Tool
Starting from current version it is possible to use a M2E Pro Plugin for a popular Import Tool - Magmi.
You can find it in the directory following the way \app\code\community\Ess\M2ePro\Model\PublicServices\Magmi.
After installation of this plugin to your copy of Magmi, M2E Pro will be able to receive a notifications about Magento Products changes during an import of your Inventory to Magento via Magmi. It will save a performance and decrease a passivity of M2E Pro actions.
Also there is no need to enable Track Direct Database Changes option for usage of Magmi Import Tool.
More detailed information you can find here.
Improvements
The same User Interface for all Integrations
The concept of the same User Interface was applied for all Integrations, so Amazon and Rakuten.com Integrations Interfaces were changed for more similarity with eBay Integration Interface:
It gives an ability to use the same skills to work with any part of M2E Pro Extension.
Channel Orders are always Imported to Extension
In previous versions there was an ability to enable/disable Orders Import option in Account Settings.
Now this option was removed due to technical reasons. So there is no possibility to disable Order Import.
Note: This option does not have any influence on Magento Orders creation Settings.
QTY Reservation is required if Magento Orders Creation is enabled
Earlier when ability to create Magento orders was enabled, you were able specify value Never for Quantity Reservation option.
In new version of M2E Pro Reservation value is required if you enable Magento Orders creation option.
It is connected with solution of issue with high number of false Quantity Revises in case Magento Order was not created.
Required Reservation remove several possible variants of overselling.
For example, Magento Product has QTY=10. In Account Settings it is specified to create Magento Order when Payment is received and Reservation is disabled (value “Never” is set).
1 Item was bought on eBay, but it is not paid yet (so Magento order is not created and Magento QTY is still 10). The next synchronization will change eBay Quantity to 10 (as magento Quantity is 10).
In this case physically there is 9 Items available (as 1 of them was already bought on eBay and eBay order was already created), but there are 10 Items available for sale. So it can cause overselling.
Default Quantity Reservation period is 1 day in new version. So if 1 Item was bought and Magento Order was not created, Quantity will be reserved, so in Magento it will change to 9 and overselling will be prevented.
Note: For all Users the settings will be changed to default values (Reserve Quantity For 1 Day) automatically. So if in your Account Settings Magento Order Creation option is enabled and Quantity Reservation value is set to Never, it will be changed to 1 Day.
Fixes
Many fixes of Mozilla, Safari, IE browsers
In new version several issues with usage of M2E Pro in Mozilla Firefox, Safari and Internet Explorer browsers were fixed.
Some serious Performance improvements
Several improvements of M2E Pro Performance are made in new version:
In earlier versions a high number of unnecessary Revise/Relist/Stop actions used to be run. Now it is fixed.
Revise of changes, that were made in any of the Integrations, was improved, so now it is running faster up to 10 times.
Total code improvement is provided to make Extension work faster.
More stable Servers Connections
Connection between Extension and Server becomes more stable, so it decreases number of error messages like “Server is currently unavailable. Please, try again later.”
Removed
Version less than 4.1.0 are not supported now
Support for M2E Pro versions bellow 4.1.0 was removed.
All Users with active version lower than 4.1.0 were notified 3 months earlier via email.
The ability to upgrade from such versions is removed too.
Note: In case you need to upgrade your M2E Pro from version 4.1.0 and lower, please, contact our support support@m2epro.com.
Please note, all versions of M2E Pro up to 5.0.0 will not be supported from the 1st of September 2015. We recommend Users with active version 5.0.0 and lower to upgrade your M2E Pro to the latest version via Magento Connect Manager.