Steve Gardham: "Without having seen the pics wrist straps would surely make the rapid direction change, needed on the anglo, difficult?"

RE:Not at all. For the "bellowsing" itself - whether rapid direction changes or delicate tone articulation - the important factor is stability, meaning that the connection between players *arm* and the instrument is safe and direct on both push and pull (and that as little effort as possible is wasted on carrying the instrument)
For that particular purpose (=bellowsing)it does not matter if the handle is located over the hand or over the wrist, it works just as well.

In principle however it IS an advantage that the bellowsing is executed by the arm as much as possible and NOT by any structures of the hand.(This is a fundamental ergonomic rule for distribution of static and dynamic work)

Now - you also have to "finger" the instrument for "playing" however..

The major disadvantage from the Anglo/Duet handstrap is that it locks the fingers.If you just had 2x10 buttons to deal with stability can be offered as well as enough range - but for your wide range instrument as you have testified yourself the need reaching awkward buttons at the same time as controlling the whole box and doing the bellows-work causes problems. The hand rather be lifted above the endplate surface ( just like Chemnitzers) and the best way to create stability is by locking the thumb with a thumbstrap. Then the rest of the hand may slide a little on the wrist support BUT still be kept in place by the wriststrap. You can flex in the wrist to reach awkward buttons and will get a wider accessible range on the keyboard this way than with the trad handles.

It is all very elementary from an ergonomists viewpoint. Just as simple as putting a shaft on an axe...