FortuneJack offers 25 free spins just for registration from what I can see on the homepage of the site, and
BitStarz also offers 180 free spins on registration as well. If you're just interested in playing and/or testing out the games on a casino, some casinos allow you to play via play money or tokens like
FortuneJack or
Crypto-Games. Good luck!
As far as I know FortuneJack will require you a little deposit before giving you free spin. I am not sure though. I remember last time I checked it and saw this kind of requirement.
I think as far as gambling sites free spins are concerned, these just have no values as you cannot earn much from free spins. Free Spins and free satoshi don't have much impact. I think the approach should be to use the real money to play gambling as that's the only way to earn good from it.
If you want to just test the site or just wana play for fun, then these free spins can be useful to you.