I have both the Harmony M and VH K. I don’t think one really sounds better than the other, but I prefer the Harmony M for ease of operation. Also for me, the built-in VH on my Yamaha, Ketron, and Korg do a better of harmonizing my voice. I’m not a “ power singer” at all, so I’m sure many singers would disagree. I use the keyboard’s internal harmonizer for low volume gigs and stand alone units for high volume gigs.