I'm not going to comment anything about the site, I think it's pretty clear that it's a scam. The difficulty is so high that even with all the computational power that is been used for mining bitcoins around the world, that exceeds the consumption of Argentina, it is ensured a new block is mined every 10 minutes on average. Do the math and use your common sense.

Now this is a misconception. How do you define free? Wasting energy is definitely a cost.