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's good for who has many BTCs. If you really have much money in Bitcoins you can deposit it, let generating interesting for few days, withdraw your initial investment and keep the site generating income for you with the money the site already gave to you.
This way you don't need to worry about lose your money on medium-long term, if something goes wrong you will lose only the profit, protecting the initial money this way.
I dont think that it is a good idea of doing this way to earn, because what if the site breaks down and all your investment BTC are gone so for little profit you cannot risk your high investment it is better that if you go for trading in any exchange you can earn more then 10% daily without risking so much. So as per my view is not to take risk for 4% interest better go for trading and earn better.