I have one gripe with the JP line (and I hear it's a problem for some other MM guitars, including basses). That's neck stability.
It doesn't affect all guitars, but those with mahogany necks and ebony fretboards are awful when you live in a climate where humidity and temperature vary dramatically through the year.
The problem is that ebony is a very hard wood and mahogany is relatively soft. The neck is very thin with no reinforcement. So when humidity rises, the fretboard absorbs moisture and expands, with frets pushing against the wood, and the whole neck assembly curves towards the strings, aiming to get a back bow. So every spring till summer I gradually release the truss rod (until it is totally released with no tension), and starting fall till winter I tighten it.
That may not be a big deal actually if you have enough room to keep the truss rod active, but in my case it came to back bow during the second year, so it became unplayable. When I took it to the tech, he saw an MM and said, "Neck problems, huh?" Then he looked at it, nodded and pointed to something I didn't notice - the fretboard was thinner around the 12th fret! This means that the neck assembly already showed a tendency to back bow at the factory, and they just made it even by sanding the "extra" wood out! And we're talking about a BFR guitar, by the way. So, I sort of got off easily because he took off a little fret height and I have decent neck bow, but if the problem gets worse, that'll require serious and expensive work or buying a new neck.
Replacing a neck may not help as they all have the same problem. The two permanent solutions require serious modifications - drilling holes inside the neck and inserting carbon reinforcement rods, or making the truss rod a double action type, or both. Really, this should be standard from the factory for these necks!
Anyhow, this long story isn't to discourage anyone from buying these guitars - they are great in every other aspect, and, depending on your climate and some luck, you may have no problems whatsoever, but be aware that there's a weakness built into the design.
So, when you buy it, look at/measure the fretboard thickness along the neck. You can see a big problem by observing the dots - if they are closer to the top surface in the middle of the neck, the fretboard was heavily processed at the factory to remove the back bow by a crude method, which isn't a permanent solution, but just hides the problem temporarily. So if you see that, return it immediately.
Despite having this problem, I still love my JP and don't regret buying it overall, mind you.