When they promise you high profits in a short time, they are ponzi schemes...they are always ponzi schemes.

The only reason a company would offer to pay you interest is if they can make more money (bitcoin) off your money (bitcoin) than what they are paying you. In this world it is currently impossible for any business to guarantee a return of even 1% per day, often these sites promise to pay much more and they usually require you to keep your bitcoin with them for a defined amount of time. This lock in requirement makes it easier for them to build a base of investors before they evantually disappear or stop responding, without you being able to withdraw your investment.

Run away from these companies. Just invest in Bitcoin buy owning it.