Bonus Buy
Bonus buy (also called feature buy or ante bet) lets you pay a fixed amount to trigger the free spins round instantly, skipping the base game entirely. The cost is typically 80x to 100x your bet but can go as high as 500x for premium features.
The math question everyone asks: is it worth it? The short answer is that bonus buy doesn't change the RTP. If the slot runs at 96.5% RTP in the base game, the feature buy is designed to return roughly the same percentage over time. You're not getting a better or worse deal. You're just compressing your session into concentrated bursts of volatility.
The real danger is the speed. You can burn through your bankroll dramatically faster when you're spending 100x your bet every few minutes instead of grinding 1x spins. Bonus buy is banned in the UK precisely because of this. If you're going to use it, set a strict limit before you start and stick to it. No exceptions.