I have one, recently acquired along with an FM3a (the only lens I have for it, as yet). Physically it seems well-made, the aperture and focus rings have a high-quality feel to them and the lens, to me, seems to sit "just right" on the camera. I've only put two films through it so far, though (with one waiting to be developed), so I've no real basis for assessing its optical qualities yet aside from noting that it seems pretty decent.
...Mike