I remember seeing an infomercial on that 15+ years ago. I think it is super cool! I don't think it would cause any harm and I believe it would be fun for many kids. Hey, the worst that could happen is that DS is practicing math arithmetic tricks instead of daydreaming when class is too slow for him.
I am a very mathy person (mathematician) but not a human calculator. The tricks I saw were nice ways to do that, just mental math. I have to think hard to see if I still remember what I learned. I did not have access to the book by then, so I am just going from the show I saw (they showed people adding and knowing how much their cart full of groceries would be, etc.).
I do NOT think it would confuse a smart kid.
