I'm not sure I'd call it a TW-90 "copy". I suppose the basic look of the grinder might be said to have been inspired by the TW-90, but there's no ratcheting tension mechanism, no drive wheel based tracking, it has two tool slots, and takes 1.5" tool arms. It also looks like he got a bulk discount on gas springs, all of which are upside down, IMO. The gas spring for the "tilt assist" does seem like a nice idea, I suppose, though lowering the motor mount relative to the tilt pivot would likely also help things.
As for the quality of the machine, I have no knowledge or opinion on that.