These aren't the famous Takumars though. The best of the M42 mount Takumars can still hold their own today, the 55mm in its various forms is a particularly popular one.

In the 1980s Pentax brought the name back and used it on a range of cheap K mount lenses as "Takumar Bayonet". These had simplified coatings compared to the full SMC and in some cases were evidently designed to a price rather than a quality. These lenses have nothing in common with the M42 Takumars other than the name.

Gritty focus is usually just that - sand or grit in the helicoil. If it's stiff but smooth you can often improve matters by adding a few drops of light oil and working the focus ring a bit, this should soften the grease again without the hassle of a complete stripdown, clean, and re-greasing (which is a pain as you need to reset infinity focus).