The buy price is calibrated to the feature's average payout: pay 100x for a bonus round that returns about 96x on average and you have compressed hours of base-game spins into one purchase at roughly the same expected loss. Some titles publish a slightly different RTP for bought bonuses than for the base game, in either direction; the info panel is the only reliable place to check.
What changes most is speed and variance: a bought feature is a single large-stake event, whipsawing a bankroll far faster than base play. That acceleration is why several regulators, the United Kingdom among them, prohibit the feature outright, and why it deserves respect even where it is legal.
Why it matters
Bonus buys concentrate an entire session's risk into single clicks at 100x stake. Knowing that the price is calibrated, not generous, keeps the feature a volatility choice rather than a perceived shortcut.
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