Echo1 Troy MRF-S (or similar size/function) advice?

A buddy of mine built a cut-down M4 smg w/ 4" daniel defense rails from a kwa M4 that suffered a terrible calamity. I'm in love, and it's perfect for a body backup in case my primary goes down.

With only two weeks until Southern Comfort, I walk in my local shop and they're just pulling the titular weapon from a Fedex box. A surplus GI sling w/rail sling mount puts it right where I want it on my side. The guys rave about it (for what it is...good range/accuracy, bang for the buck i.e. good for an echo1).

So let me lay this out there; I'm buying this tomorrow after work...but should I commence upgrading, and if so recommendations (metal upper & lower would be nice), or buy/begin workup on a visually similar weapon of higher quality? Remember I have 2 weeks, then Irene in a few months. (FWIW I've read /watched a lot of reviews, nothing I didn't notice/learn in the shop but I'm no tech and I certainly don't trust salesmen).

My specs: Field & CQB use, (range followed by accuracy) FPS limited to say 360 w/ .25g (gun in shop shot 350) Short (4"rails or equiv.) Battery in stock. I prefer nunchuck/lipo combo e.g. the kwa m4 stock as I have lots of both, but buffer tube is tolerable. Budget say about $400 for the short timeframe, unlimited for afterwards. I care not about trademarks. Need attach point for ris light, foregrip, flip sights/optic, two sling points.

TIA