Free mining sites? Please keep off from those sites , there is nothing good to write about them. Mining takes a lot of resources, hardware, software, mining pool, electricity cost and maintenance . And someone said he is doing it for free. Watch out, I guess they just want traffic to their site.
I've already agreed they are probably complete scams, but just to play devil's advocate, why would anyone want to draw attention to themselves if they are outright stealing? In my naiveness, I had thought that maybe investment money went to pay for all that equip and electric, like crowdsourcing. I looked into actual mining and it is indeed not cheap and not for the novice.
If there was an honest start-up with that in mind, I'd go for investing in it, as I myself don't have the brains to put together a mining platform. Nor do I have the money, but if I knew someone with the brain part I'd chip in. (At this point, I'd have to know them really well.)