Rated 4 out of 5 stars

Finally, a very good calendar and task sync!! Works great with Lightning once it was configured properly! Installed the RTM Android apps quick and no problem. Task/Calendar sync is quick and works great. I paid Remember the Milk the $25.00//yr for the Pro account, worth every dime. Would like certain improvements, thus no fifth star but an outstanding start!

The only annoying thing is that sometimes you get an icon next to the calendar name indicating that: Calendar XXXX is temporarily not available. When this happens the read-only flag is set to true and you cannot save to the calendar until you clear the flag via the calendar properties. Then however, calendar changes saved locally are overwritten by the server on the next sync as if that save local didn't really happen. When the previous happens the calendar in Lightning is slow to non responsive as is an event window if you have it open. Otherwise is works fine

Note: The above paragraph is no longer an issue:
Been using the latest version for a couple of months and creating events (not tasks) in Lightning and then having that sync'ed to RTM works fine within the constraints of the common shared fields.

Updated 6-12-15
Still very pleased with the functionality as implemented. Can create calendar (event) items in TB and have them sync (upload) to RTM. The new calendar items do go to RTM and then sync down. No data loss if you add items in TB first.

This review is for a previous version of the add-on (0.3).