[mcguyver]

I would buy pre-assembled no doubt. If you've worked on an AEG before, you could do it, but there is very little about these guns that resemble a Marui AEG that you could quickly find yourself scratching your head.

The tutorial on Systema's site is a definite help, but I could see that a part could become damaged during installation and you won't find the replacement right at hand.

Unless the price difference is huge (like half), I'd go with the pre-built. At least you know that it was done right and tested before you get it.

BB misloads are common on any AEG and are frequently caused by dry or over-engaged hop-up. The hop-up on the Sytema needs to be lubed as does any other. Systema recommends after every 300 rounds, but more likely that's a typo. 3000 is most likely the right number and Marui calls for every 10,000 as an example.

Buy the Systema if you want. I have no objections, obviously. But to make the gun truly a universal weapon, invest in the cylinder kits as well. The gun was designed for 500 FPS, or 300 FPS if you have to.

The only thing I would upgrade would be to change the 15 amp rated Tamiya (or 10 amp Kyosho I think on the M4) to a 30 amp Dean's connector. It's a superior connection and all AEG's should use it, but few do.

If you have yet to see a Systema, check with Dave's Surplus in New West. They had one when I was in there 2 months ago and they still may have it.