I have a Keltec SU2000 in 40. Not a bad gun to have with 22 round Glock mags. I wouldn't buy another one. I am surprised they didn't just jump to 10mm or 45 ACP to be a little different.
S2Ks are simple blowback, 10mm would be a bit much for a simple blowback gun without making the bolt mass ridiculously heavy and/or the recoil spring too stiff to operate easily.
Is the Ruger PCC simple blowback as well?
Edit: looking at pictures, I think it is.
Edit edit: From ruger
Dead blow action features a custom tungsten dead blow weight that shortens bolt travel and reduces felt recoil and muzzle rise. Bolt is machined from heat treated, chrome-moly steel to ensure strength, structural integrity and durability.
I think they're using the word dead instead of simple, sounds more tactical