Hi Draq
I shoot the usual stuff too although living in Sint Maarten at the moment, macro is king. I've done just over 70 dives with my two Primes.
I've got the bumpers, the neoprene, the wide-angle diffusers. the protection ring, one reduction ring + reflector, one supercharger .... and one LSD. I must be Oskar's delight!
The Retras are almost pieces of art and to let them get all scuffed up and scratched is more than I could handle: hence the bumpers and neoprene.
The protection ring is useful as the glass dome of the Retra stands out in a convex curve beyond the depth of the housing. The protection ring protects this when the strobe is, for example, not in use and standing glass end down drying or whatever.
The reduction ring you need if you use the reflector - which is especially good for quick TTL grab shots.
Wide-angle diffusers do as they say and I use them nearly all the time for WA shots.
The supercharger is terrific if you are using the LSD. I powered through the batteries (Eneloop Pros), pre-supercharger, easily into the battery red zone on a two-tank dive with the LSD. Not an issue with the Supercharger.
No hesitation in recommending all of them.