FWIW Larry, I use the Harmony M. Nice and easy, especially if like me, you only want to use say one, or at the MAX, two "harmony" voices. Although using midi data it can go to four voices.

It has the adaptive algorithms as well that pick up on your vocal and applies auto adjustment...can be used as a stomp box or with a footswitch if you want it on your keyboard...

Good thing about external boxes is it means you are not "tied" to the one keyboard....

PLUS - being pretty much discontinued you will get good deals on them! But they still sound excellent, even if discontinued.

Dennis