I had a go with a couple of games on my PB631, and think that Towers didn't want to accept my right solution (bug of the puzzle, whatever....)
Anyway, that means that the app runs ok on the device. No crash, no display problem, fine for HD.
I also did a quick search on github for "pocketbook". I got 294 matches. Many are not relevant (several e.g. seem to interpret PocketBook as one of several variations of a chinese electronic wallet app for android), but there are beyond the three links mentioned above. Maybe you were there too.
For instance, I ran into this, which appears to
implement a button with low level drawing operations. Which is anyway not a proof that an API method is missing.