I have owned a Newburgh era one, and still own a later MusicYo era GM7TA.
Overall they are great guitars. Some things to consider as compared to an Iba type guitar (since we are on a Iba/Jem website). The necks are Les Paulish with a profile sort of between a 50's LP neck and a 60's LP neck if you know what I mean, not Wizardish at all. The frets are also small like a Les Pauls, definitely not jumbo. The transtrem is a neat idea and works okay, but it is a trem, so it isn't 100% in tune in every position. Down one and up one are pretty close, and the rest will sound fine to your ears when set up properly. If you look at a tuner too much though, you will go crazy.
Some caveats to consider when looking at used ones. The transtrem is bearing driven and most you see on ebay will not return to neutral exactly. Yes, there is a little arm that locks it in place, but the things EVH did with one on OU812 (summer nights) probably won't turn out like you would hope. Your best bet is D'Addario only strings since they recently (within the past 5 years) calibrated them for the Transtrem (TT). And, if your TT isn't set up correctly, it won't transpose at all.
But, the graphite neck is more solid than a wood neck when it comes to tempature and overall it is a very solid guitar. If you are handy with work on guitars, they are a neat challenge to set up.
I bet you discovered steinbergerworld.com and their accompanying Yahoo forum. Lots of information on those pages, but it isn't as hot as it was 5 or 6 years ago when MusicYo was still producing new GM's. The Synapse and ZT3 have sort of slowed the pace of postings there, but there is still great info and the forum community is pretty mature and stays on topic.
Anyways, enough rambling, hope that helped some