Don't bother buying any parts till you actually have an AEG and using it in a game. Till then expensive or cheap stuff like this is not required.
Why you ask? Well let's say you are one of those folks who last out 2 years of waiting. You get in and decide you like the feel of an AK. Then all the M4 parts like that one will be stuff you're selling at fire sale prices.
Or you find that it doesn't fit your brand of AEG, or if you buy one and it breaks but the company that made it has shut down. Or KJW isn't building that M4 any more, or Ken is selling RC Helis when you hit 18.
No part of this spells a winning plan.
Airsoft, where nothing is hurt but feelings.