Masterkey-tm ??

[Maaaven]

Does anyone have an opinion on this tool / toy / gizmo?

http://www.mymasterkey.com

It is a sort of a musical slide rule that is an aid in
scales, chords, modes, and transposition.

Thanks in advance.

[Chris Fitzgerald]

I think it's like a set of flashcards, and that it would be better to simply internalize the information. If it can help you do that and you can afford it, cool. But in real life playing situations, you don't get to stop and look stuff up.