I have one, bought it for $45 at a camera shop in excellent condition with case, caps, etc. I don't expect I would get half of that back if I tried to sell it here on the forum as a virtually unknown off brand m42 lens. Performance is alright but expect significant fringing in out of focus high contrast areas under bright sunlight.
I don't use mine much because I bought a Vivitar Series 1 70-210 f/3.5 a few months later that (other than being larger and heavier) is much more convenient for most shooting.
Here are a couple of samples to show fringing, let me know if you want more of other scenes.
Overview
If you go to "All Sizes" on the photo page linked here that will get you to a 100% crop.