The instruction to play the completely symmetrical concertina in an Asymmetrical manner seems dogmatic and irrational. The analogy with violin bowing when speaking about 'bellowing' makes sense though - because fine qualities of tone are controlled by working the bellows. Doing this with just the right arm however, can be looked upon as a result of desperation, not knowing how to manage both the carrying, bellowing and fingering of the instrument at the same time. None of the tutors describes how to use only the right arm for bellow movements while standing, and the instruction does not appear in tutors for the Anglo or Duet concertinas. Neither do the authors present a motive for the horizontal position of the forearm while playing standing, nor the background of the instruction to move the bellows in a straight line.
Many players obviously do otherwise.
Support' may be separated into some factors, which are more or less integrated. The concertina bellows usually is quite flexible. The more folds and sides the less stability and control. The early six-sided English treble concertinas had bellows with four folds. Later ones usually have five or six.