I had an old and very cool nine-button made by Mr. Hebert in the late 60s. The metal trim was cut from venetian blinds and it was painted black with a brush. Cool or what??? Sounded great with Binci #2s...
Except I use(d) the 1 button all the time. Play on the pull and start stretching for a second note up the button board. There are all sorts of cool tones. Plus, the way I mic'ed my accordion with a gooseneck sax mic one each side, when I hit that one button, I got a killer tone.
Nine button accordions -- a great idea for a hammer dulcimer, but YMMV and no problem.