I *think* I know the types of groups you mean coalport - I've been to one group devoted to one particular instrument, and found 45% think they're rockstars and play as individuals (not ensemble members), and 45% are just not that musical. I hope it doesn't sound too snob-ish to say the lack of ambition and self-awareness is depressing.
However, given the complexity of the theremin/matryomin, I struggle to believe Mable could be one of these groups. Whether or not you approve of the style, surely there's some skill in playing in harmony (or perhaps even more difficultly, unison!) on such a difficult instrument? Hearing multiple heterodyning instruments form a group is certainly something unique in this day (unfortunately contrary to what Leon Theremin envisaged as the future of music), and the quality of musicianship makes it enough for me personally to think it's something worthwhile for the 'outside world'.
I've only played matryomin very briefly (about 3 weeks after I even got a theremin), but found it easier to play than any other theremin. Given the funds, I'd love to try to make it world in England; I think if we're good at anything, it's being eccentric!