This site makes a lot of giveaways with good and expensive prizes, but most of giveaways were left without winners. Gleam.io service disabled their contests for few times, and it should be serious reason to do that. Also when i asked somewhere in the comments at donthatethegeek.com about the fairness of their giveaways they have not answered. Instead of that they banned me from commenting.
So i think at least their *giveaways* are scam just for increasing quantity of subscribers and visitors.