Several Las Vegas casinos have done a promotion similar to this, including Riviera and Palms in 2012. Worth playing at Cosmopolitan if you're in town. You must have a net loss for the day, so watch and redeem for free play as soon as you are down $100. This is mostly for higher limit players, but even 25c players can have a bad run and get reimbursed (if they don't give up first). Offer good till the end of August.

One strategy is to play a single $100 bet on a slot machine and hope to hit a big win. If not, you get your money back. Value of the play is almost $50 if there aren't any other restrictions. Some clubs require a certain minimum time of play to minimize the single-big-bet benefit, but I don't see that in the Cosmo offer.

As ususal, this is a promotion to attract new players, so you must get a new Players' Club card to participate. And you can do it only once. Bring a friend .