I never bonus buy. Did it once with 15 times in row on Deadwood (big bonus), never made it past the initial price of the bonus buy.
Karen and Prison were a huge flop for me
Rave with xbet had me like 1 Bonus every 15 spins on avg, 4k spins, never past 400x tho
Tombstone was a solid 10/10 with xbet, made it twice 4400x within 800 spins, but since then - nothing.
I stick to Gulag and Hoarders, every now and then some Mental and that's it
Only thing I noticed with the xbet thingy: the bonuses are "always" low af compared to non xbet, but that's just my subjective impression
What else are you playing though? I find it's hard to find a game that I enjoy burning my money on