Just swap my Yamaha PSR1000 with KORG PA80 with a good friend and do some evaluation.

I was surprised that the fill-in button does NOT advance the variation to the next variation. This is a very typical use of the fill-ins. Granted that sometimes you just want to fill without advancing but it is quite rare and I can always hit the variation button to switch back. Also, because of this some of the fill-in seemed to be mismatched with the variation style.

With KORG i30, you can program the fill-in button to advance or reverse the variation style. With Yamaha, there is a button that allows automatic fill-ins when the variation button is pushed and selects the appropriate fill-in based on your next variation and the previous variation.

Am I missing something ?

Not only that. But the registration memory is awkward to use. I have to press 2 buttons: first the bank and one of the buttons near the screen to select a registration.