If you look at one, or pictures, you'll see it has two external extractors - one on each side. I think the multi-caliber function was one reason behind having two extractors. They enabled one slide to work with cartridges of different head diameters by holding the case centered between them.
I also heard that didn't work so well.
I have some SA catalogs around here somewhere, and I think it lists them in 38 Super, 10MM, and 45ACP; with 5" or 6" barrels; and maybe ported or non-ported. It seems like they were rather expensive at the time.
Peters Stahl of Germany designed/made the unit. I'm pretty sure it was also sold by someone else, either before or after SA. Maybe Pachmayr?