Bonzo3legs: I don't think concertina players pull faces any stranger than any other musicians, although we anglo players in particular seem to do the thousand-yard stare very well.

Regarding bellows control and dogma: I play duet (Maccann and Jeffries system) and anglo and handle each of them differently according to size, weight and reed response. To my mind, good technique is whatever allows you to make the music you want to make, without limiting or injuring the player.