I just dropped in here by accident after having being out for quite some time so I can't control myself from whipping my hobby horse once more:
The handles of concertinas - both the English type and the Anglo/Duet type are tremendously primitive and dysfunctional from common ergonomic points of view but it is quite easy to improve conditions a great deal.Of course there are several ("bad") playing habits which may be dealt with and at best avoided but as with any other handicraft or instrumental work the most important issue mostly is to fit the task ( = the instrument itself in this case) to man instead of trying to fit man to the task.
The common 5 mm ( or even less) concertina buttons are too lean for comfort and easliy cause pain, impressions or numbness from repeated or constant pressure. Press buttons in general should be 10-15mm diam for good comfort.That is the case with most telephones, calculators, computer keyboards, control panels etc. The concertina constructions mostly admit at least 6mm, Anglos often 10mm diam buttons. It is hard to see any reasons not to reform instruments in that direction.