The pricing shapes are different
A subscription is flat: you know the monthly cost before you start, and the vendor absorbs the usage variance. BYOK is metered: the platform fee is small and fixed, and the provider bill scales with your usage.
For light and moderate users, BYOK often lands below the price of one subscription. For people who consistently max out one model every month, a flat subscription can still be the cheaper of the two.
Flexibility vs simplicity
Subscriptions win on simplicity: no keys, no provider accounts, no usage math. BYOK wins on flexibility: one interface for GPT, Claude, Gemini, and Grok, and the ability to switch models mid-task.
The trade is real in both directions. If you only ever want one provider's models and value zero setup, a subscription is the simpler choice.
How to decide
Pick a subscription if you use one provider's models heavily and want a flat, predictable bill. Pick BYOK if you use more than one model family, want to cap spend yourself, or prefer your keys stay under your control.
If you are unsure, estimate your monthly token usage with a cost calculator and compare it against the subscription price for the model you would otherwise use.