Freebies or Giveaways, most gambling sites are offering this thing. Their only goal having this is to attract players/gamblers, it is obviously for newcomers who will look into that but I don't think it was a good idea and I don't rely on such promotion but to consider most on their legitimacy even they can't offer those freebies, free spins.

Well, I hope OP could make a list of only those sites that are worth trusting, not because they have such attractive offerings.