Thre are duets and duets.

I play McCann duet for morris -- not very well, possibly, but I get by. This is the "too many buttons" duet, but the right hand is simple enough to play. The left hand (to me) is not very intuitive. Umm, that's a tactful understatement; what I actually mean is that (as the man who sold it to me 25 years ago explained it), the fingering pattern seems to suggest that Mr. McCann labeled a whole lot of birdshot with A through G, shot that into a hexagonal piece of wood, and used the result for the fingering pattern.

The concept of the duet is that you're supposed to be able to play a duet between the left hand, which has the low notes, and the right which has the high. On the McCann, I've never gotten to the point where I could do that freely; I still have to memorize all my left-hand fingering patterns.

However, I've also got a Crane (Triumph) duet that I'm starting to learn. Unlike the McCann system, which is played with four fingers per hand (making it possible to play quite fast), the Crane is a three-finger system. This makes it more suitable for slower tunes than fast (but it's fast enough for morris, I think), but the great thing is that this means it has the advantage of identical fingering patterns for the left and right hands. the first time I picked up this instrument, I found I could actually play a duet between my left and right hands.

Hope that helps.