Nah, they're rubbish, don't touch it.
But do give me the seller's details so that I can rescue anyone else from buying it...
Seriously, if it's working, then I'd bag it at that price. I had a play with a JG MP5, it was fine: decent FPS, consistent and accurate. It was the version with the integral silencer and for a wonder the silencer was actually functional too, you could barely hear it.