These sorts of sites are all HYIPs (High Yield Investment Programs) which are ponzis.

They started in the days of e-gold, now they're in bitcoin.

They'll run for awhile, pay out early investors with later ones (classic, textbook model).

If you think you can get out the door before the hammer falls, go for it (but that's the model).

Eventually they all go down the tubes (and "eventually" usually comes sooner than you expect).

They also attract DDoS attacks like nobody's business.