Maybe I'm confused on the diatonic/chromatic thing. Doesn't diatonic limit you to essentially one key.? I'm thinking for example of a diatonic harmonica where you need to grab a different harp for each key.My main use for this is for playing rhythm back-up to folk-blues-gospel 3 and 4 chord stuff (plus a few 7ths and minors)in the more common guitar keys C, G, D, E, A etc.