Those offers from Whale.io look decent to me. The wager requirements are not that bad and the Bonus Buy can pay off big if luck hits. Since you have little experience with slots, trying demo mode first is a must before risking real money. Watching gambling streams is also helpful to see how these games actually work. However, slots are pure luck anyway so winning is never guaranteed.
With those good offers together with opportunity of trying and playing with demo mode, it's very good for users to try and get experience with games in demo mode. If they feel good with game experience in demo mode, they can consider to take action with their money and accept these good offers from Whale.io.
In gambling, surely there is probability of winning and losing, and even an offer is bad, you can still win, while with a good offer, you might loss in the end. Be aware of it will help gamblers and users are more careful with their decision making on what to do with their own money.
No guarantee but with good offers, why don't give it a try and see how it goes with small fund first?