Basically, in Balkan area our accordion players use this system. Actually, only in Balkan they use 6 rows of buttons. This gives you more ways for fingering. It doesn't matter which key you play song in, fingering is always the same. Not like piano style keys. Also buttons are much closer to eachother than piano style keys. You can play much faster with less practice. But, at the end , if you really know both ways are good.

Sorry missed Mirza's post.... i was saysing that 6 buttons from the former Yugoslavia (balkan) but thats what he already explained...