Their metal bodies are good. Fit and finish is excellent, as you'd expect from Marui. Not as tight fitting as the old school Systema bodies, but they definitely fit way better than any Classic Army, G&P, King Arms, VFC, etc aftermarket body that I've ever used.
There is no "export model" of any Marui product. At least not from the factory.
The build quality of the mechbox is still superior for an out-of-the-box product, and still industry leading, in my opinion. The new hard recoil engine mechboxes are completely different than the old v2, so you could say that changes have been made in leaps and bounds.
Upgrading to higher velocity is a bit more of a challenge, due to the added complexity of the recoil/blowback system. It also does not take standard AEG parts, but there are plenty available from a number of Japanese aftermarket companies. I've upgraded a few to 350-400fps.