The small keys are okay for soloing, as a few organs on the market, several years ago, sported a third keyboard with smaller keys that were designed exactly for that...however, on the organs there was a coupler that allowed you to assign that uppermost keyboard voice to the manual below, allowing for playing the selected sound using normal sized keys if you wished.

I had a Yamaha CS01 like Donny, and it was only for solos (and bass lines), and rightly so, as it was monophonic and played one note at a time, max. The small keys weren't an issue for that very reason.

I found chording on the KMA (and other similar sized keybeds produced and discontinued by Yamaha many years ago), very awkward, and especially so if there was another keyboard with full sized keys involved in the setup. Intervals were obviously different, and I found the benefits of the smaller mini keyboard (smaller footprint, easy transport, very light weight) not enough to choose it over a mid sized PSR or Roland that hardly were heavyweights and offered far more playing enjoyment.

Still there are those who love the KMA and, I can see why...it just isn't something I'd use.

Ian