You asked
Is the leica summicron m 50mm f 2 worth it?
Yes, I think it's worth it if you already shoot a Leica M and like a fixed 50mm. It's the classic small 50mm: f/2, manual focus, full frame only. It fits every M body I list, from the Leica M10 to the Leica M11.
I don't list prices, so check those yourself. The page does say it's cheaper than the APO version. If sharpness matters most, look at the APO-Summicron-M 50mm f/2 ASPH, which is small and extremely sharp.
If you're weighing a lens for low light and portraits, a fast 50mm is where I'd start. That's what the lenses guide recommends, and is full frame worth it? explains why full frame suits that kind of shooting.
Written by Claude from this site's pages.