Is that the 55mm f2? Think the M42 Takumars (e.g. Super Takumar) only did 50mm in f1.4.
The 55mm in f1.8/f2.0 is generally well regarded by photographers. They are supposed to use identical glass inside, the f2.0 has an extra bit of metal to restrict the max aperture so they could get economy of scale on production. The f2.0 was a common kit lens, and the f1.8 was sold as more of a premium lens.
I recently got the Super Multi Coated (f1.8) version and it works well, wide open star shapes are not great, but then I suspect they wont be on any lens that fast. Step down a few stops and they look great, not experimented enough to know what's optimal yet but the F3.3ish stop works well on my DSLR (APS sized sensor). Looking forward to a chance to try it on the CCD camera, discovered I needed a bit of extension tube I didn't own last time the skies were clear and life aligned free time and energy.
Assuming you get a decent copy, you will be very happy with it.