Don't mistake me...it's not that I think the VFC mechboxes are sub-par or prone to failure. They function quite well. My comment that I'd simply drop in a mechbox was more along the lines of...if/when the stock mechbox goes down I wouldn't bother fixing it up piece by piece, but rather would just buy a complete mechbox and drop it in.
And with the VFC...you have that option of just buying a complete mechbox and dropping it in....whereas with the KWA you don't.
I've built/worked on/tuned/upgraded plenty of mechboxes...but I'm at a point now where I just wouldn't bother for my own gun.