I've used Gon's BT implementation. It's mediocre at best. Lots of connection drops on Mac OSX have been reported. But tbh, I haven't seen any good BT implementations in custom keyboards (and Gon's is likely one of the better ones).
My big problem is that for me to support BT, it needs to be minimum Windows/Linux/Mac and have virtually no issues. Not to mention having to deal with batteries and charging.