why don't you post the actual lens you have queries on and see if anyone here has reviews? or at least post the mount and the focal length you are looking for? note too that some FSU lens don't have that accurate a focusing on modern non-FSU bodies due to slightly different dimensions of the helical or something like that, can't rem. but pt is, the lens may be good but it can't focus properly on the body also no use.
Most FSU are M42(screw mount) len and obviously it will mount and focus correctly on M42 camera. With adapter, it will mount on many camera. On Nikon and maybe 1 more brand (Minolta? -- not sure), the SLR has a different design from the regular brand and their OEM adapter for M42 have a glass on it in order to focus to infinity. So the len is the same only the SLR mount design that need a glass to compensate which is on the adapter. Most people dont prefer extra glass and it maybe cheaper to get a M42 camera or another SLR that no need glass on the adapter.