The Ballone Burini marque was two brothers who split. One of them is making a 27 key that goes from low "G" to A. Personally this would be unusable for me, as the folk genres I play all use the high "B" extensively, even if you can get by without "High C."
My favorite treble config is 30, up to "High C" on the top and down to "Fiddle G" on the bottom. But I use 26-keys whenever I can get away with it--"High C" on the top and "Middle B" at the lowest. Because I love the smaller size. Irish trad is fine on a 26--the small minority of tunes that go below "Middle B" don't usually linger down low. They'll hit the low A, say, and go right back up, so it's easy to arrange around that. Scottish has a minority, but a not-teensy minority, of tunes that spend some time down below "Middle B." All those "King George" tunes, or the "Miss Lyall" strathspey and reel, have a low, growly A part. If I know I'm going to be playing some of those tunes I'll use a 26 key LMM and switch on one of the registers that has both Low and Middle reeds in the mix--LM or LMM. And just keep my hand in the octave where I do have enough notes. Nobody in a sesh or an audience is gonna know the difference.
But klezmer and other Eastern European genres really need that low Bb, A, and G. French musette and tango also benefit from that access. For that kind of stuff I'd really rather have 30 treble. For castrato-octave passages that go above "High C" i could care less, don't need those notes making extra dimensions in my accordion, will just play them lower. It's not the classical repertoire, after all.
