Android, although being pretty damn good mobile OS, has a few shortcomings compared to IOS. And Freedrum pretty much falls victim to multiple of them:
Until recently, there hasn’t even been a “pro audio” API on Android and that means we can’t really get good, low latency on many devices. Have a look here for a slightly depressing read: http://superpowered.com/latency
Bluetooth MIDI uses the newish Bluetooth LE model, and that’s notoriously shaky on Android. It also has some inherent latency (7-15ms) which is a pretty long time when you want to hit a drum. There is however one thing you can do on some phones that might fix the problem: Turn off WIFI! Yes, no kidding, this sometimes helps, even on high-end phones.