I've seen prediction websites before, I think, so it's probably not the first one. But in any case, I don't think I know a reputable solid website with this, so it's not like the niche is full. Why only 60 seconds, though? How about long-term predictions, have you considered adding those?
It's good that there's a demo mode. I tried it and have a suggestion: why not allow people to place the bet while the previous round is going, in advance? Like in crash games. Because the window is very small right now. And why just 3 abstract betting options "long, mid, short" rather than betting on particular prices with a certain plus-minus something range?
This is a nice way to pass the time, as a round lasts only 60 seconds.
On which exchange is the price based?
Based on their Introductory video, the price comes from Coinbase, Bitstamp and Kraken.