1. Its not all its cracked up to be.
2. It is VERY operator dependent. The machine is, as all are, stupid as a one legged crow in a squaredance. The operator has to really know his neck/guitar geometry in order to make it work right.
3. It is also VERY dependent on the correct, and totally immobile mounting of the guitar in the cradle - something that takes some doing. That is - when you try to get things set up to say .002 or .001 inches... even temperature and humidity play hell on what you're doing. So do the very least of movement, even movement caused by the vibration of the machine itself.
What this all means is... in "theory" it can do wonders, especially with crowning. In practice, its really no better than someone with a bit of knowledge and practice can do - assuming real world working tolerances.
And remember, it does the fret tops. It has no control on the fretBOARD, and its straightness (or wavy-ness).
The PLEK machine, in the hands of someone who REALLY REALLY knows their stuff, would be pretty good. Any shop who forks out the bucks and thinks they can say "we have a PLEK, so we're good!" is full of prunes. They gotta be good first. The Plek just makes it easier to be good.
Its like CNC. When I was back in the gun biz.... and we'd convert 1911 frames to accept "whale tail" grip safeties (which I hate with a passion), there were places saying they did a better job, because they cut the frames on a CNC mill. I can tell you, they didn't do a better job, because the variation in frames is such that they still had to go back and "fix" the work the CNC machine gave them, and the fixes were obvious. OTOH, I fit all mine by hand, one at a time, and the results were such that it all fit together quite nicely and it didn't look like a one-size-fits-all job.
Don't shop the process guys. Shop the RESULTS. What you want is the end result. If its good, it matters not how it got that way. Thing is, a good man can correct things, see things, measure things... the PLEK machine wont pick up. Get yerself a good man to work with, and if he has a PLEK, and can use it... great. But if his hands are his tools, thats great too.
On a final note - the PLEK to me, is like the modern player piano, digitally controlled, and perfect in many ways, and totally devoid of soul. It still sounds like a machine. Nothing beats the real thing, and the life that hands give to the performance.
And thats that.