This is a wonderful app to solve the puzzles featured on the channel, however, there's some key features in the web app that are missing from this. Notably, the letter function, the extra colors, diagonal lines on the line tool, and the new fog of war mechanic are missing. The latter is, albeit, quite new, but seeing as this hasn't been updated in 11 months, adding at least some of the new things would be great. Additionally, the ability to detect if a solution is correct for irregular or otherwise "non-normal" sudoku puzzles would be most welcome. When I do complete one of those, it is often marked as wrong and therefore incomplete, so I usually just delete it from the app.
Overall though, it works superbly well for almost every puzzle!