Sorry for the late reply! We did this in our first MVP actually, and the result was that giving more choice over model selection resulted in worse retention / usage over time

Each models have their own behaviors / use cases (we're using Gemini now), and by opening it up to everything we needed to allow users full control over the prompts (even with defaults), which increased the learning curve significantly (and the usability of other features like Voices)

Ultimately decided to go with generous (i.e. Unlimited) paid plan