I’ve played over 3,000 matches with Shredder. It’s flexible, powerful, and has most of the bells and whistles. The flexible game save function is helpful, and the leveling mechanic is reasonable.
The biggest downsides are 1. The move suggestions, at least at my (middling) level are laughable. Follow them and you’ll win every time. But if you back up and try the same move on your own, without triggering it as a hint, you’ll be slaughtered. Meaning, when Shredder is teaching you, it sets up unrealistic responses that allow it to make successful hints. This is, in fact, the opposite of helpful. Even at my level, it was immediately obvious that the suggested moves were idiotic. 2. The puzzles are of little use, as they only test your knowledge. They do little to help you learn more. There is no explanation for why this or that is “...the best move for white”. And because it’s also timing you and scoring you, it feels judging, not supportive. When you fail, you just move on to the next puzzle, you don’t learn anything. It’s frustrating. Finally, the visuals are quite dated at this point, though that is obviously subjective and minor.
All in all, it has a lot going for it, but really shows weaknesses as a teaching tool.