I asked few questions on GMS forum regarding Android exports. I think you might be interested.
What I've found out:
1. GMS Android exports are fully native.
2. IAP, AdMob, Push Notifications are built in.
3. Performance is not perfect. You still have to be carefull with sprites etc. and do some optimizations.
on a reasonably modern device - should be fine
Well, C2 Crosswalk export is actually perfectly fine on modern devices <img src="{SMILIES_PATH}/icon_e_wink.gif" alt=";)" title="Wink">. So things are a bit cleared out, but still question is what "fine" means comparing to C2 export. We'll see after they sort out things with server overload.
Here is the topic: http://gmc.yoyogames.com/index.php?showtopic=676728