Fun Fact: Not every game has the same multiplier/a fixed multiplier. chain-bet bets are playing with a 1/16 chance to win. 2/20 is pretty good for a 1/16 chance to win, but it's a very very low sample size and cannot accurately reflect the house edge/chance of winning.

Also, they do have an house edge, since they take BTC from your original bet. Send 0.01BTC? It's a 0.0098BTC bet to them, which adds up to a house edge. The house edge varies based on bet size, but there definitely is a house edge.