Well when you go on the website there's hardly any details about their actual service, just how to give them money, and that's pretty suspicious.
Plus the layout is the same as I've seen on scam sites before, I think.
Definitely not as obvious a scam as all this crap with promised returns, but I would stay away if I were you, could be a Ponzi.
That's not actually true. They do have a full FAQ section on their website.
Also, a Ponzi scheme is a fraudulent investment operation where the operator pays returns to its investors from new capital paid by new investors, rather than from profit earned through legitimate sources. xCoins is a Bitcoin escrow platform who charge fees for matching buyers with sellers, providing verification and acting as a middleman for the trade, so I don't think you can really compare them.