Sometimes I get 20 free spins and usually I get nothing, but this time luck smiled on me... out of 20 free spins I got 8 euros. I continued to play "Aloha King Elvis" with that money, hit the bonus round, and went to 18 euros. I moved to Wild Spin and I got a nice win after 10 spins:
It's not bad! The rollover is x40, which is ok since I got just 0.00013 BTC from spins and I need to wager "only" 0.005 BTC. With a bit of luck, I will finish this bonus and maybe have some balance left.