Does this stuff make much sense at sessions which normally feature other genres? The other players have to catch on to some unusual scales, key shifts and tempo changes, which takes a few rehearsals. A couple of tunes from the repertoire of "Moishe's Bagel" (Edinburgh klez group) have caught on a bit round here, but that's about all.

An English concertina can't produce much of the rhythmic oomph this sort of music needs - it would substitute reasonably well for a violin but that's all. You need to find yourself a backline.