"I got my M249 Para about 3 weeks ago as a heavier alternative to my MK17.
First, the positive: this gun feels great. It's got some heft to it as it's full metal, and despite the polymer front hand-guard, it does not feel cheap by any means. The design is very good; it's easy to access the batteries and there is lots of room in there. The quick-change barrel means that you can easily replace the barrel or make adjustments if you need to. The carrying handle seems reasonably strong; I don't run with it holding the carry handle, but it's nice for transporting it around between matches.
The provided battery is okay, you'll get more performance by running a lipo on this gun, but I found that it was adequate for a few hours of gameplay.
Rate of fire is very good; I've found that this gun has been very accurate for me considering the shorter barrel on this model, and as a result it's fantastic at suppression: you just never stop firing.
The downsides: the wiring is garbage; it's very thin and the provided fuse is very low quality. I'd recommend upgrading the wires and switching the deans. At least tape up the fuse (if you don't upgrade the wires) so that the connections don't slip out and short your battery (as they did with mine). Also, and this is a minor gripe, but because of where the hop-up is located, it's hard to adjust it easily on the fly.
Other things you should know: the Para version of the M249 is far more wieldy than it's big brother. However, it still weighs quite a bit. You'll want to purchase a sling for it and be aware that if you are a smaller player you may have issues carting it around if you're playing a long game. By no means is this the fault of the gun, it really comes down to player preference. Also, if you're laying down the fire (especially on the stock battery), you will run out of battery power pretty quickly. I'm used to playing a DM role where I can run the same battery all day. That's not the case with the M249.
All in all, I love this gun; it's scary on the field, especially if you're on the receiving end, and the quality of the product is overall very good out of the box."