Of course they are vague and secretive about what they do, but they do claim to "put your coins to work" presumably in some way that will generate a profit.
Also there is not written that it is legitimate ways of generating profit. We can only guess at the moment.
Because the site deals in Bitcoin it is okay for it to be a Ponzi scheme?
But in reality, they just use your money to pay out previous investors.
And I would not say that it is a ponzi. Again, these are just guesses.
There is not a single shred of evidence that they're actually doing anything to earn a profit with the money you deposit.
Also, there is no evidence to the contrary.