So it is just like a normal betting site like a local bet where you should find another person to bet on the other team?
Yes. If you place a bet and nobody bets against you, you get your money back (no fees).
It sounds cool but I don't think that there would be a person who would bet on an underdog when the gambler wouldn't have an advantage,
I mean why would they bet on a team with a low chance of winning if the profit on betting on a stronger team would be the same?
We've also thought about this and you are right.
I believe that more "balanced" bet evets are better for this kind of p2p betting (e.g., the champions league final).
If a team has a high chance of winning you might want to place a larger bet on this team to attract more people betting small amounts to take your money.
It's like betting a larger amount on a team with odds 1.15. You risk more but the chance of losing is much smaller.
On the other hand, those who bet on the underdog are like e.g., betting in a team with odds 12. They have a much higher risk but they might not care because they bet small amounts.