Harmony M is really good. I have one in each of my two setups. I tried Perform VK a couple of times, and it is really good, but I get along better with the older M.
Interesting. The VK is newer and looks to have soft feel buttons instead of footswitches so I'm curious why you like the M better. Just more used to it ?
The VK has more options, especially if you download extras, but with more bells and whistles you make things a little more complicated.
I use mine 99 percent of the time with one voice above, some reverb and the automatic e.q. processing.
I use a standard foot switch to bypass the harmony, the same as with VK.
It is easier for me to turn knobs if I want to change reverb or harmony levels than it is to press and hold buttons.