It depends.
For LF Lenses, their BGN rating is usually pretty darned good.

For 35mm bodies, it can make a big difference. They also seem to grade 35mm bodies on cosmetics ONLY. Therefore, a body graded EX will look good but may very well have a mechanical problem. Maybe, it depends on brand. I've never had any luck trying to buy used Nikon Manual focus 35mm bodies from them and, believe me, I have tried many times. I have given up and will not buy 35mm gear from them - nothing but trouble and endless mailing stuff back and forth.