The bonus buy reality check: what 100x actually gets you
The buy button is the most expensive feature in the game and the least understood. Here is the arithmetic behind it.
The price
Where it is permitted, buying free spins costs 100x your base stake. At $1 a spin that is $100 for one bonus round. The purchase has its own published RTP, listed separately in the game info, usually within a fraction of a percent of the base game.
That "roughly the same RTP" is the crux. It means the buy is priced fairly. It does not mean it is a good idea, and those are different claims.
What you are actually buying
A round of 10 free spins with multiplier bombs. The distribution of outcomes from that round is wide: plenty end below 20x total bet, a minority land in the hundreds, and a very small number produce the results that make the feature famous.
Since you paid 100x, a round returning 40x is a 60x loss in about thirty seconds. Readers describe this repeatedly, and the surprise in their accounts is consistent — the expectation going in is that a purchased bonus should at least roughly break even. It should not, and it does not.
The compression problem
This is the real hazard. A $100 bankroll at $1 spins gives you 100 spins and a session of some length. The same $100 spent on one buy gives you one round lasting under a minute.
Expected return is similar. Variance is not remotely similar. You have taken all the risk you were going to take across an evening and resolved it in a single event — and if it goes badly, you are done, with the entire session ahead of you and nothing to play it with. That is the position from which people deposit again.
Where buys make some sense
For a player with a bankroll large enough that a single buy is a small fraction of it, and who has decided in advance how many buys the session includes, the feature is a legitimate way to skip a base game they do not enjoy. That is a narrow case, and it is not the one most buy buttons get pressed in.
The rule worth keeping
If you cannot comfortably afford four consecutive buys that all return nothing, you cannot afford one. Four bad rounds in a row is not unusual — it is an entirely ordinary sequence for a high-volatility bonus.