It's an RSR Transitional , which the bible says is rare . It states that rare is 2-400 pieces . I have a 6590 that I bought NIB here years ago . It's sort of a hybrid , it even has a bushing like the 1st gen's . It's all in the eye of the beholder , depends on what he's asking . I don't know if you can search on GB , these guns aren't seen too often .
I'm sure it's just me and like yoke vs crane but these are not transitional. The transitional and pilots were in the standard prefixes of the time and were stamped Mod 659 or Mod 459, etc. but were mostly 3rd gen.
These were put together for RSR a few years after the 3rd gens were introduced. From the SCSW 3rd
RSR was a "major distributor" according to the SCSW 5th addition. As snw19_357 notes there isn't a lot of information about them. Most were 9mm, a couple of models were .45.
I have a friend who owns one, but it's a shooter without box or accessories. I think that only ANIB guns would have collector value.