I think no reason invest again in this HYIP, because needed to many time for get doubled coins.
Yes you shouldn't consider this as a main source for regular eranings. Therefore the time it takes is to unspecified. And big investments take way to long. But i use it as a nice little source for some side income. I once send the earnings of one day faucet earnings to the site and now i'm at 0.002 that's 10x what i invested. I think that's good for about 2-3 months.
Aren't all of these side income ?

If you put in like 500BTC it's surely not and you could lose a whole lot of money. But for the most it's a side income that's right. I am using it to double my faucet pauyouts. So nothing, except time, to lose for me there.
How can you lose your time?

??
Do you mean to lose 2 minutes to make a payment?
If you have, for example, 10 free BTC on your account, you can put some of BTC, for example, 4 to doublebot.com
After N time you will receive 8 BTC back.
If your BTC will lay in the wallet or in DoubleBot, you lifetime will flow the same speed.
The only difference is that in the DoubleBot your money will be locked for a time, but after that you will have 14 BTC on your wallet instead of 10 BTC.
If you are not going to spend all your Bitcoins (or at least more than 6 BTC, which will left in your account), while it is invested, there is no difference where will your Bitcoins will be. I think that DoubleBot is much safer than lot of web wallets.