I own the SL II. Focussing ring stiff, but smoothening after some use. Excellent compact walk around lens. Wouldn't reccomend to use it on bigger cams, though, too small. ;-)
Concerning lens generations:
SL I = w/o cpu
SL II = w/ cpu
SL IIs = afaik same as SL II, just with "retro" look similar to Nikkor AI.
Something special with my sample:
I own several Zeiss ZF.2 lenses (= w/ cpu), the VC SL II 40 mm f/2 and the VC SL II 90 mm f/3.5.
All other lenses are treated like AI-P lenses by my cams, i.e. advanced metering modes like the high light mode in more modern Nikon DSLRs are not supported - of all the manual non Nikon lenses the 40 mm SL II is the only one supporting all metering modes of my D750.