An excellent purchase. I loved my M6, and do miss it...especially when I'm lugging my Pentax 67 around.
The 50mm is a great lens, and well worth picking up if you see one for a good price. It's a bit shorter than the 75mm, so it collapses very nicely into the body, making for an even better travel camera. I'm not sure I ever took mine off until the day it was sold.
The only thing I wasn't a fan of was the meter, which tended to under-expose a little. Angling it down 20 degrees seemed to help, but I found my hand-held meter a bit more consistent. I had the earlier 'non-MF' version, so maybe it was improved in your later version? I'd suggest burning through a test roll to check the meter in different lighting conditions before taking any important photos.
Enjoy!