Well, I've only had it for one evening (post England beating Germany), and I'm very happy with the M904E as it's so much gun for the money. I paid £170 for it and I suppose the closest AEG I've held / used that's a direct price comparison is the G&G CM16 FFR A2 which costs £165 and has an electronic trigger and standard MOSFET, but that piddly £5 difference gets you a programmable MOSFET + slightly higher FPS out of the box + higher RPS + quick change spring (my son's G&G Firehawk feels terrible in comparison, I think I know what he'll be asking Santa for).
I bought Nuprol 1300 mah 11.1v 20c LiPo's to go with it, and in semi spamming the trigger I can't come anywhere close to outracing the gun which put a big smile on my face. No problem with the PTS EPM 1 mags either.
I did a quick chrono on 0.25's and got around 295 FPS / 1.03 J, so I suppose around 330 FPS on 0.20's so not bad out of the box. I've a Maple Leaf Macaron 60 degree ready to swap in, I'm not expecting any FPS improvement from it but better grouping, so next pay day will be time to play around with springs (although the buffer tube seems to provide slightly worse access to it than the PDW stock from photo's, in that there's less light getting into the tube to see what you're doing) and maybe think about a slightly tighter inner barrel / better hop-up unit.
Something worth noting is that the cover for the quick change spring protrudes a little into the buffer tube so a long battery does stick out. Also I wish the buffer tube had a sling plate on it like most other M4's, a very small thing I suppose, but it makes the gun hang lower on my sling than I'd like it to.
Edit 1: Had more time to fart around with it now on a fully charged 11.1v LiPo and with the Maple Leaf 60 degree in it. Getting around 308 FPS / 1.08 J on 0.25's now and way tighter grouping.
