The whole "let's make an Android device for seniors/the blind/whoever and pin it on an ancient Android version/spec it really low but charge a premium" thing is unfortunately not new.
If you look at the Blindshell 2 and 3 you see plenty of this happening as well, not to mention way more expensive hardware like the BrailleSense Polaris which last time I checked ran on Android 5, scary "Mind updating right now please?" Google Play warnings and everything.
If it helps any, Talkback does have a set of keyboard commands it responds to, perhaps making your keypad buttons fire those means the implementation might be less brittle but given what you've already had to deal with maybe just not touching it ever again might be thebest thing at this point :)
Disclaimer: Actually blind Android user/developer