Don't have a review, but I can touch on some points.
TM internals are fine. Only upgrade I'd consider right out of the box are metal bushings, and that's just for peace of mind. Run in stock configuration on an 8.4v like all Marui aegs are made for, probably won't even need the metal bushings.
Hopup was quite nice. Much better than the M4/M16 style. Using .25s I could easily shoot past 150 ft.
As to the externals, yeah, largely abs, like nearly all Marui aegs. It is a better quality plastic than what is found on JGs. You can always get a metal receiver in the future too. I didn't feel mine needed one though. Do note that the cocking handle is not strong enough to do the "HK Slap" repeatedly (none of the airsoft G3s are). If you don't know what that is, don't worry, you shouldn't use it with an airsoft gun anyway.