I made M a little while back, and boy did I not feel ready for it---I thought that I could only consistently shoot A-level. (And occasionally B. )
Went to a couple of majors, however, (A3 and Nationals) and found out that indeed, I was ready.
If you practice classifiers to get good at classifiers and make M, that is one thing. But if you practice shooting and then on classifiers make M---then even if you don't feel like you shoot M-level all the time, you will still be shooting well enough to run with the M-folks.
You may not be winning but you'll be in the right crowd at the end of the match.
I have realized I can shoot nearly as fast and as accurate as local GM's. I just can't keep my head on long enough to be consistant. Another thing to work on.