~When it comes to bonuses and promotions then expect that house would be always at advantage.
They cant just be offering on something that will really be costing them money but rather they would be finding ways on luring in players to make money.
The advantage of the house is over all the players on the site combined. All those players will certainly lose from 1% to 10% of their money to the house. But 90%+(and usually it's more than 95%) will be returned to players in the form of wins and bonuses, and it is absolutely not necessary that everyone who's winning or getting bonuses will eventually lose it to the house.
Well, if you chose to bet more thinking that you could win additional profits, most likely all your gained profits will eventually lose and goes back to the house. I guess thats another strategy from the house that they will give you chances to win profits at first and when you bite that chance, then they will start getting back slowly the money you have won.