Marui's are reliable, but not as durable as some players desire. I'm sure the G&G will be mostly metal, with plastic composing nothing more than the stock.
Marui, on the other hand, uses plastic like it's "goin' outta style". Sure, I bought a Marui M4 for it's reliability, but ended up spending alot of cash to eliminate the (A) BS. Today, the only plastic Marui piece is the sliding stock!
And who's to say the Marui will be so much less expensive? Their latest AEG offereings are comparable in price to much better, ALL METAL airsoft guns by companies like G&P, G&G, and Classic Army. I think TM needs to pay attention to this trend, because we are living in the day where people actually PLAY with these guns, and need something more durable! If they cannot adapt, I see a dim future for TM!