what's your opinion about BTConline.io? Is it a scam?
Not just a scam but a very obvious one as well. They're offering people a free 0.0003 BTC per day just by signing up. Just use your common sense here, how is this profitable for them at all?
At some stage they will ask for your deposit/investment in order to withdraw the funds that you earned for free, and they'll simply eat that up and exit scam. That's usually how the scam goes.
There has been countless examples of the same scam strategy in the past and this is just another version of it. Might not even be a ponzi for all we know, it could just take your money as soon as your deposit rolls in.