The name Giant is only a brand, so it could actually be any number of 7 different sizes.
One concern some will have is that the frame is aluminum, thus susceptible to premature stress cracking. Aluminum work hardens with repeated impacts and vibration. I have a gt2-a frame, and have not had issues. I attribute that to the well balanced engine and solid mounts.
Also, the frame diameter may be too big for the engine mount. I would not want to use the alternate mount on an aluminum frame. It's a little U-bolt that could crush right through the frame. There is another mount made for large diameter frames, and I believe sickbikeparts sells it. Worth looking at if that's the frame you decide on.
The engine, I know nothing about. It may be a winner for all I know. If you're somewhat mechanically inclined then I'd tear it down upon receipt and clean it up before installing it. I would also look in to balancing it. It doesn't take much. A small, accurate scale and some time is really all you need.