Sorry I didn't get to read all the previous posts before posting
I'd just like to add in, the whole reason why marui is the standard, and why it will always be the standard is because;
1) They were the first, at least the first to patent the mechbox (proof is TOP uses the bellows because they weren't allowed to make the same mechbox design as marui)
2) The first upgrade parts ever made, were made for the first airsoft guns ever made, the marui.
3) people copied marui's design since the bellows were crap and copyright laws aren't so hot in Hong Kong/China, so new brands were inherently TM compatible
4) The whole upgrade part market is primarily based around the marui standard, 2 dozen profitable upgrade part manufacturers, and half a dozen high quality airsoft manufacturers aren't going to conform to any other standard since it's a waste of money.