Good on you for asking. Their Web site essentially admits it is a Scam:
"*Cloud mining should be considered as a fun, recreational activity and not a source of income or investment. The above numbers reflect no difficulty increase. Investing involves risk, including possible loss of principal. "
To get your money back in 660 days requires 9.5% increases in difficulty every 12 days. They have been running 16% in 2014. At 16%, the return on your $2100 investment drops one cent per day in 660 days at which point it will have paid back $1,330.
