Steve:"I haven't looked at the website yet"
RE:I suggest you do before having a serious talk on what you say:

" My problem is one very large heavy anglo. .. I can reach all of the keys and use most of them but after more than an hour's playing my hands get sore on the straps"

RE:The "Anglo/Duet concept" is fairly stable in two dimensions but not for counteracting a 'rotation' of the instrument - if looking at the endplate clockwise at a view from the right.
The "Chemnitzer handle concept" wouldn't help much since there it is presupposed that the instrument is steadily resting on both knees, or riding over one of them.Furthermore it works on pull but very poorly on push ( one reason that Argentine tango is performed 90% on pull with the Bandoneon)

One point with "my handle" is that the thumb is fixated passively (and this does no harm since it isn't employed for fingering anyway) instead of being actively engaged in stabilizing duties meaning harmful static effort.

Another point is that the Anglo/Duet "handstrap" locks the midpart of the hand and thus obstructs flexion and extension by the fingers. Fixating the wrist( as with my handle) - instead of the knuckles - by using a "wriststrap" liberates the fingers but to also admit a suitable position of the hand a "wrist support" ( similar to the platform of Chemnitzers) lifts the hand 20-40mm above the keyboard.