I have a Hohner Pokerwork which has this keyboard layout (with an accidental button at the bass end of each row). Some people have the thirds removed from the chords - or have a stop fitted to allow you to include or remove the thirds which gives the instrument a lot more scope.

My Pokerwork is currently gathering dust as not long after I got it I "discovered" the Anglo Concertina, which I found suited me much better.