The Version 3 mechbox is a pretty cool design.
The first time I tried to put that trigger mechanism back together I was swearing up a storm, but after some practice it became pretty easy.
What I really like about the V3 is the motor cage and how much it helps in doing proper motor pinion to bevel gear alignment. It also just feels solid.
That said, what I dislike about the V3 is the ambiguity in shopping for parts.
I know very few people who are really "into" AKs, yet most of the motor cages and selector plates on the market are AK ones, even though I see far more G36s around. The fact that these parts differ between various guns that use the V3 gearbox makes me less confident in shopping for those parts than if I'm shopping for M4 (V2) parts. I've also been burned on cylinder head compatibility. The Modify G36 cylinder head sold on airsoft parts completely does not fit into the JG G36 mechbox. The head has an extra piece of metal for which there is no matching space in the mechbox.
So if you're tempted by the V3 design and are looking to buy what seems to be the least-expensive, most common, easy-to-get, and most-frequently-upgraded G36 in Ontario, the VA36/JG36, you're going to need to know some of these quirks.