My opinion is that most of these lenses can produce acceptable images, but are hardly stellar. The worse aspect is the color fringing, blooming in wide apertures. Flare is also not great with most of these lenses. For me, any focal length longer than 135mm is not easy to focus critically, and a tripod is really needed. Using manual focus lenses for moving objects is asking for frustration. I think that OEM telephoto lenses have an upper hand over most of the third party cheap equivalence, but that's not to say there aren't good ones. One example is the Soligor C/D 200mm f2.8, and the Vivitar 200mm f3, which is quite good when stopped down a bit. Also of note is the Vivitar 135mm f2.3, which I had for a while but never really used much, but nevertheless a really good lens. Tamron is considered more upscale with its Adaptall lenses. The 135mm f2.5 is a decent performer.
If my experience is any indication, most modern cheap zooms are at least as good, if not better than the cheap 135mm f2.8 or 200mm f3.5/4.5 telephoto lenses. Sure, the zooms don't go down to f2.8 or even f3.5, and the build of the old lenses are way better, but if image quality is not there, they are just nice paper weights.
Salute! - NEX-6 & Vivitar 300mm f5.5 @ f8. Note purple fringing on right. Click for larger.
Allen Garden - NEX-6 & Minolta MC 135mm f3.5. Click for larger.