I think if he choos a low volatility slots, $100 wagering isn't that hard. It means he just need to wager a total of $100 and is not necessary to deplete $100 bankroll. Betting on Dice may probably needs $15 to fulfill that $100 wagering at a 98% chance of winning, maybe a little less on Plinko.
Calculating with that statistics, I believe it is worth a try to get 50 free spins since at a minimum bet it cost $10 plus the potential to win bigger amount.
According to the rules of the bonus that included on bonus. You can only received the 50 free spin when you play on
participating slot games. You have no choice to play on low volatility slot game or less house edge game like plinko and dice. Duelbits know how to give fair bonus because their reward has no wagering requirements. They will become a foundation if they give bonus without wagering requirements while the requirements itself can be claim without any possibility for them to have a profit.