I think the base is slightly smaller than the mount base, yeah. I need to try it on my Spotmatic and see if it wobbles there as well.
It is quite sharp, yeah. I spotted some somewhat pronounced CA as well as some of the sort of hazy out of focus areas I sometimes see with other older M42 lenses, but overall I'm pretty impressed.
Though the wobbling is quite disconcerting when the lens is in use, gotta say. It's very slight, but when you're used to a solid lock it feels much more pronounced.
I think my Helios 44M is superior optically, but it's a close race.