I have started playing a D/D# in the "normal" keys, which I think is quite abnormal. It works particularly well in "Irish Em" (mostly or all Em and D major chords in the tune). Bm and A tunes do not work well. For G and D tunes there is a lot of push-pull; however, there are a lot of changes where there is no problem with the sound if you are a little off with the most difficult move: changing button and direction at the same time. In fact I think it gives you a very nice sound like a grace note.
The fingering is no problem for me at all, but again I am abnormal. I spent years and years working out fingering for playing Irish reels on my piano accordion, so doing it for a button accordion was not a terrible ordeal. I will say that it was not easy and that it took some time, though.
I have not tried to play bass with the button box. I can play plenty of bass when I change to my piano accordion. Also, at this stage of my playing I can easily change back and forth between piano accordion and button box.
Why D/D#? I guess you can say that it started out as a mistake. I liked the D row because of my piano accordion background and a background playing a diatonic harmonica (blues). I had heard that D/D# used to be played a lot; however I didn't know about the Eb part.
My email is firstname.lastname@example.org. I live in the San Francisco bay area: USA.