I have one that I picked up very cheap from KEH or eBay several years ago. It's at least as good as any of my more modern EF primes. The only prime in my lens collection that I can confidently state is definitely noticeably sharper than that 50mm f/3.5 is my EF 135mm f/2L (which is definitely the sharpest lens I own).
I haven't done a ton of scientific testing or anything, but I do have a tendency to pixel peep. I wouldn't hesitate to use this 50 for copy work or negative digitizing.