I am currently typing from the Fxtec Pro1 X, using Android.
It's great for me with the stark exception that it has recurring issues with dropping signals, be it mobile 4G, Bluetooth, or WiFi. I would not say that it makes things unusable at all.. just occasionally annoying. It's usually fixed quickly by switching to airplane mode and back.
The most annoying part is that I can very rarely use it as a telephone unless I'm on WiFi. People report they can't hear me at all only very broken and garbled when I'm on mobile signal (T-Mobile carrier). This seemed to have been resolved by my using my smart watch to make calls which appear to go through without issue.
Freaking love the keyboard on this thing though, so it's worth it for me.