Thank you for the detailed explanation,now I understand it completely.Still a great offering I would say to people who can permit to risk 1 or 2 Bitcoin as I don't see any banking interest to even come close or compete with such return for one year if you put let's say a Bitcoin with price 43.000 USD you get as an interest after a year 1754 USD as a reward.I would love to see a bank which can do that as in Europe I know for sure there is none,but may be there is in US I don't know.
Do not forget that you are investing in bitcoin, and not any other fiat thing. So, basically if you invested 1 bitcoin today, at bare mimum 4%, that means in 20 years that will be around 2.25 or so bitcoins. That is bitcoins, not fiat, which means your bitcoin could worth 1 million dollars during that period as well, so you would have invested 45k or so worth today, get 1 bitcoin, and in 20 years you would have 2.25 million dollars instead while all other 1 bitcoin holders would have 1 million dollars.
I believe the biggest increase you could get was 4.40% interest, and that would basically be 2.4 or so as well. So all in all, you will keep on making money while your money also gains value in itself.