That’s a decent challenge considering the minimum bet, target multiplier and rewards complimented to each other.
However, the game listed in there are high volatile especially those freaking Nolimit city slot games. Even with the lowest minimum bet which is 0.5$ will result to huge loss for someone that will chase this challenge with limited bankroll.
Challenges open for everyone but people have different conditions and risky tastes so that they can accept the given challenge, join it or ignore it. They can join challenges for fun without solid plans to win, just try their luckiness while there are some other people can join challenges with clear ideas and plans on how to increase their chances of becoming one of winners.
It's not 100% surely winning the challenge but can help them having higher chances if they are experienced enough with past challenge participations as well as they have plans for their participations and generally they are very possibly afford to lose money. Gambling is risky, joining a gambling challenge, a tournament is more risky but nobody forces anyone to join. It's freedom to join, and after joining, let's be fully responsible for your action and result.
The rewards is competitive compared to other casino challenges.
Rewards for challenge's winners are important to make a challenge attractive enough so that it can have enough participants and marketing effects for the company.