I really like the mechanics included with this chess. I spent the $6 or so dollars to get unlimited hints and undos then i came across a big issue. There's been two separate occasions where the hints and the AI react in illogical ways. The hint tells me to move a piece a certain way which is surely a bad move where the AI can counter it but then the AI choses not to. So now I regret spending the money to get the full game. The app has been really good otherwise.