I have now talked to Dave Farnsworth and can confirm that, in his opinion, my Mae West is indeed an ASR version, he has kindly allowed me to post the information that he sent me, see below:
The Mae Wests you describe sound like the type used by the ASR branch. I have had perhaps 6 or 7 of these over the years and all conform to the same basic pattern you describe. Variations include examples with and without a neck zip and some have no provision for use with a bladder (kapoks only). Those with bladders would appear to have been orally inflated only (no CO2 cartridge/lever). All of the ones I have had were simply made and without rubberisation internally. Some had AM marks but none were labelled.
The example you refer to in the Armourer Article actually has brown webbing tapes (the print colour makes them appear darker) the same as some on one of my own standard '41 patts. I still have that one in the stockroom somewhere if you need to compare......
A couple of the ones I have had came directly from ASR crewmen and I believe Mick Prodger also had some similar examples from ASR crews. I remember discussing this with him many years ago and he told me the photos he took of them came out with a blue 'haze' giving a misleading appearance.
I have always assumed that these were a late war introduction in order to save on materials and that they were not produced in large numbers. Certainly the vast majority of photos of ASR crews indicate widespread use of the standard '41. I'm guessing that the AM thought that these 'stripped down' versions were adequate for the ASR branch as they worked from the relative safety of their launches rather than the aircrews who could end up in the sea miles from anyone or anything.
So that clarifies it for me! :-)