There are some websites i know that really gives people opportunities to be mining BTC and I believe this to be true. It can be mined with this platform and can be withdrawn but this does not mean that it is really as easy as you are thinking.
Normally it's might takes up to a month to be able to mine up to $4 worth of BTC and you are to tap on your mining button on hourly basis which you have to be active all day and night.
From my experience on the platform , I believe the best way you can be able to earn a reasonable earning is by referring people and these people you are referring must always be active at all time...
A lot of people are taking this as a business and probably they are making a lot of money with this , you could be able to earn up to $3 if you have 100 active miners.