I think that would be the first negative review I've heard of one of those. I think the tuning issues (if you had one) could be solved easily. Probably depends on how high gain. I have a Bernie Marsden and it gets high gain great.......enough for me anyway. I play 80's gain stuff. Not sure about the modern metal type of stuff. These are even tough to find used, so I think that says quite a bit about them.
Don't know about the two issues mentioned; however, I've sat with one and it was a very nice guitar. Extremely light, neck is unfinished and felt really good (although I prefer a bit bigger neck). If funds were available, I'd certainly pick one up. Bought my Bernie Marsden SE same day I played the ZMSE. Love my BM and its PUP's are hot.
I have one that I've thrown a bone nut, had a feet job, and run a set of prs sc250 pickups in it. It's a mean ass guitar. That's not to say the guitar played bad new out of the shop. It played well, but I abused the hell out of for year and it need some. The same pickups in my real prs and the zack m. Se Its much more bright and punchy. Great tool to have.
I have had one (the newer semi-hollow one, not the older fugly 3 pickup one) for a couple years now. Out of the box great guitar. As it sits I have a DiMarzio 36th PAF in the bridge, and I use it for high gain rock frequently. No issue with this guitar. I have another PRS SE that has SC250 pickups and it's a monster. The ZM is the first PRS SE I've owned out of my 6 that has NOT had tuning issues. Every other PRS SE I own or have owned needed a new nut and tuners right out of the gate. Love the SE line but the hardware is garbage.
<----playing Alice In Chains 'Man In The Box' through a Splawn Quickrod. Zero complaints about how the ZM can handle high gain. I initially was concerned about feedback being a semi-hollow guitar, but no issues.
Have had one for 3 months or so, sounds awesome, lightweight and stays in tune no problem, I think I saw the video your talking about with some guy with an ENGL head but through the 5153 it slays, IM not a metal guy but like was mentioned its a mean guitar and very well made.....