I'd avoid like the plague because it doesn't seem to give you the manufacturer, unless it's Lone Star, or Evolution Airsoft, neither of which I've ever heard of and buying a gun for that much, if it's made by a manufacturer I've never heard of, just seems like a bad idea to me.
That entire first paragraph is utter BS and the photos provided aren't even all of the same gun. "The ultimate realism, perfect finishing and attention to details make the Hardcore Series the most wanted item also by collectors."
Seriously? Collectors will want that? With its fake trade marks and "original" design? Who wrote that?
£300 for something where no information is given, is not worth it in my opinion.
There isn't even an approximate fps listing.
Look on LandWarrior or Fire-Support, you can get a standard looking M4 by G&P for around £240 and up and it will actually tell you what you're getting and the specs of it, instead of just listing generic crap.