I'm confident this will turn out to be a ponzi scheme, but if you invest nothing apart time then don't see a problem!
If you invest nothing, you can't withdraw. The minimum withdrawal is 0.01 BTC which is bigger than your maximum balance is you don't deposit.
It's a scam. The OP of the btc-flow thread says that everyone is able to double their coins which is obviously not true.
Yes I personally wouldn't even invest my time in something like this, but now you have pointed out you have to invest btc to withdraw its almost certainly a scam.
Investing any btc into this would be stupid or desperate to say the least! Problem is there are plenty of stupid/desperate people about