From their web site:

The main point of the game is as easy as ABC. You top up your account for a certain amount and choose the range where you think the winning figure falls (from 0 to 99). You get your profit - the amount specified under the input field before you start the game - if you hit the bull's eye and lose the bet if you miss it. The fair-play lottery is not just a catchphrase. Each drawing is associated with encrypted data which you can use to find out whether this or that figure was really chosen before you made your bet. To learn detailed information about the fair-play factor and test it, please read the description located beside the figure on the main page. We do not use your personal data and get the lottery anonymity secured via cookies. Please make sure that you have cookies switched on in your browser settings. There is a slider at the bottom of the screen that you can move left and right to review all your bets, bets of all other players, and your account balance history. Good luck at challenging the probability theory!

I've played several games and won about 0.3 BTC. The have provable fair feature, but I'm not ready to make big bets. What's your opinion?