The M50 2.0 came with my MX when I bought it in 1980, and I used it without any complaints for many years. If you can get it for a good price, why not buy it? I don't think you'll be tying up hundreds of dollars.
As Shel said, Don't get caught up in minutia and data about optics. Make pictures, look at them, and see what you like for any given type of scene. I second that. Many differences in lenses only show up when photographing lens test charts. No matter how sharp it might be, I've never seen a picture of a test chart win any prizes. Pat White
