It does not have all the functionality of Remember the Milk, but it really shouldn't. It works well for adding and completing tasks. If you need more, just open Remember the Milk directly, then "Refresh" Remember the Sidebar.

The only issue I've had is that the icon to change the status of an item doesn't load for some reason. This issue has been going on for a few months and I've just ignored it (the blank box where the icon should be still operates like the missing icon).