I bought the complete set of Maths Quest books from The Book People a while ago. At the time, they were a bit hard for A, and she did do some of them with supervision from Mr M, but preferred the Usborne Puzzle adventures which she could do herself.
However, she has now clearly grown into them, since she sat for 90 minutes solving the clues in The Museum of Mysteries. C sat alongside her - it was his job to remember which page they had to turn to next. It's a bit like a Choose Your Own Adventure puzzle book - you have to solve the maths puzzle to work out which page to go turn to. It's the most maths I have ever seen A voluntarily do, and therefore has already repaid the money I spent on it (which probs wasn't very much anyway, given it was from The Book People).
A great buy for your little mathematicians (reluctant or otherwise!) Some puzzles are harder than others, and A required some help with some of them (and she is quite good at maths, thanks to my strong mathematical genes obv), but the concept is extremely good, and it was enough to amuse both kids for an extended period of time in that late afternoon grumpy phase that children have. Well, I say children, but to be quite honest, I am not immune to a touch of the 5pm grumpies myself.