.Well the amount which you get from miner is your trading money, the money which you withdraw from them is the profit which you make by trading those assets. The trading is done at a leverage of 5 so margin gets involved. It requires a decent trading knowledge and experience to be able to withdraw from the exchange, so eventually it became a a bit difficult to withdraw. Mining is also slow your first withdraw comes within a week due to referral bonus and new account bonus but your next withdraw will be possible only afer one-two month depending on the price of btc. So the miner is more like an marketing tactic to make users sign-up with them and for people like me to refer it to others.
I also had my doubts regarding it being a scam but I have heard people were able to take out crypto without even spending a money. I am even actually glad that I found it that I found this exchange as it eventually led me discovering a lot of other blockchain related platforms including hive.
You should always do your research. But in my experience it doesn't feel like scam.
This is how my account look at the moment
Well the other 10 was ruined during China FUD
If you have any other doubts let me know I will try to explain it you at best of my capacity