The commands in the language are stable. Still waiting on full 3D.
3rd party API works, but Facebook implementation is quickly approaching its end of life (February).
Basic interpreter is solid. Only seems to "barf" when accessing arrays out of bounds, which is easier to check for with the new version.
1-c No, but mostly. I'm not sure what ones have differences off the top of my head.
1-d Some folks have issues, but I think it is firewall related. Hard to tell since I've never really had issues with broadcasting.
2 - Good performance. I've never had the program crash due to too many sprites. I think I've pushed it well over 5,000. Framerate dies, but on windows no lower than 30FPS from what I recall. It's device dependent (memory, GPU). Performance is consistent if you take out hardware as a factor, but that's always an issue. Most games built with AppGameKit have no issues with performance, other than loading times on mobile.
3 - Well... No debugger just slows you down. For debugging I write to a log file sometimes, sometimes some text on screen. It all depends on what I need to look at.
4 - no clue, but I imagine if you email their sales support that they might hook you up.
Overall it's a pretty stable engine. Great for intro level development. It's missing a lot of 3rd party functionality that is common in today's mobile games like Google Play leaderboards and other game services. Ads are locked to AdMob or Chartboost (although Chartboost pays pretty well) and you can only use a single provider. FB functionality works for login, but you probably can't get friend's lists anymore, you should be able to publish to wall still. It needs more 3rd party SDK integration abilities. Right now it's all pretty plain and old with the exception of Chartboost. Internal functionality is pretty solid.