Although not that much, I've managed to win my freebet...
But free bet wins are always small and not like using normal amount in the account to bet. Example. If you are giving $10 to play bet, the potential win is either $4 or $5 or below and that amount becomes the original amount for you to play and win big. I don't know if whale casino is also like that but I have experience such in some casinos I have participated.
Well, when you bet with any amount, the result as how much you can win depends upon the odds. The higher the odds the higher the winning amount but that also increases the risk. The bets with lower odds are somewhat safe and you have more chances to win but the outcome/ profit of such bets will be less.
However, most of the casinos will impose restrictions on free bets wins to prevent players from easily cashing out large amount out of the casino. One way to stop them is to increase the wagering requirement.