All of the Duelbits reward doesnt have a wagering requirements after fulfilling the requirements to get it. I claim promotion like this before and I remember that you will receive all the profit from the free spin directly to your wallet which is instantly available to withdraw.
They have already set a wagering requirement of $100 to get the free spins so yes there would be no such after requirements if you want to withdraw the money I think.But you have to risk $100 also but if you are getting 50 free spins then it's worth trying it if you are gambling so take the risk and who knows you get some good profits into your account.
Basically the requirements come beforehand and not afterwards. In most casino you may get something free and that makes it a lot harder because after you get that free thing, then they ask you to gamble with it and more often than not you are going to end up losing it back again until you are free to withdraw it.
However, here that is the reverse, you risk something to get it and maybe you will or maybe you won't but if you do end up getting it then that was the requirement, the second you get that reward means that you fulfilled all the requirements already to get that and this is how you could withdraw it as soon as it is credited to your account.