I like to buy bonuses as well! It's crazy when we buy a bonus and get x10! Or something similar! It's not like that just with No Limit, it's the same with Relax, Pragmatic, and other providers that have a "buy bonus feature"!
I used to buy the bonus feature, the first time I use that option is on the Money Train 2, and I was so happy when I got the persistent payer on the first roll of the bonus. But sadly it has taken me only 5 rolls because the bonus stage got busted since there is no new multiplier that appears. Then from that, I tried Book of Shadow, it was good during the 1st and second bonus buy package, but after that, the losing streak hits me.
Buying bonus feature will just save you time on spinning but it shortened your gambling session if you are unlucky on hitting proper win to make an ROI to your initial payment especially on slot games that has a very low hit ratio and RTP like hacksaw games. I rarely purchase buy bonus feature unless the hit ratio of that slot is high so that you can get atleast part of your initial payment.
Bonus feature is a double edge sword which is very dangerous if you become greedy and chase your loss by buying it multiple times without getting any profit from it.