Great thread... did not know about this lens. Just picked one up for 12 pounds.... Just waiting for the adapter ring and I'll see how i do with it!
Do you know of any other great M42 lenses that would be good on a 5D mKIII?
Just depends on what you're looking for.
For me, getting M42 lenses was more about getting character lenses than finding affordable alternatives as I have all my FLs covered with current lenses.
If you are in the same boat, take a look at the Helios 40-2 (85/1.5) as well. It has the most pronounced swirling bokeh/unique look I have seen yet from any of my M42 lenses. There is also the Zenit 50/1.7 with the square bokeh (optical formula believed to be copied from Leica) which is my second favorite.
As far as the Helios 44 models, I have the 44-2, 44m-4, 44m-7, and the 77m-4. While the latter two are newer, the swirly bokeh is definitely still present and the resolution is noticeably higher. All four have been used with both a 5D3 and 6D without issue.
The multi-coated Takumars are also very nice. Although I don't find that they offer anything unique over my modern lenses which is why they get mounted the least.