I think with bonus buys you’re guaranteed to get stung on higher stakes, with Spinal Tap and Buffalo, for me at least, £15 and £10 tend to reap much better rewards or at least longer playability than if I was to feel lucky and try £30 etc,.
Youre always better off doing a £10/15/20 bonus buy IMO, because I dare bet you wouldn’t see a bonus from £10 on 10p stakes, but you can buy one for that.