i was trained by JM Blakely he's the guy the JM Press is named after...
The JM press has proven to be a terrific movement for me, personally. It's worth learning them the way Jim Blakely does them as opposed to the form demonstrated by other lifters like Dave Tate, etc. There is a video on YouTube featuring Jim giving a very detailed explanation followed by a performance of the execution.
I was astonished by not only the amount of weight I could handle, but also the comfort of my elbows, which have bothered me from time to time; never from this, though it may have contributed to a bit of pain in my left wrist.
Regardless, I can honestly say that my upper arms have gained noticeable thickness, and my pressing power has improved at a faster rate than it has any time recently.
While Jim naturally recommends his version, he admits that other trainers have experienced good results with variations. Larry Scott most notably used a version in lieu of traditional skull-crushers. Obviously, Scott's predates Blakely's - I'm merely pointing out the comparison.