My opinion is 4% per annum is quite less for bitcoins and it is quite risky because they are doing mining business and we all know that it is a risky business.
Yes, seems very low. I just checked their 'interest calculator', it shows ~100 satoshi daily interest for the capital of 10mBTC. I am not sure it is a worthy returns for the risk of 10mBTC investments.
Anyway I just disabled my auto withdraw functionality so that I can maintain my earning within them to earn daily interest. We can conclude about success of this interest paying programs by watching how many people are coming into our service section with ref back offers.
it is on par with what banks offer ,if not more (in some countries) besides it is almost risk free
the only risk there is the site closing down,which is not going to happen,I hope
when the bankroll investments are risky,HYIPS are plain retarded to invest to and just keeping your coins in your wallet
doesn't bring you any profit
so its a win win situation-low risk,no need to do more than unticking autowithdrawals enabled box
u may even consider depositing an odd coin or two if you don't use them