Does anyone know of something like Otter but offline with tolerable performance?

Otter is the only thing approaching affordable for individuals, but I don’t really trust it given they’re playing fast and loose with user data.

Silero[0] seems to have decent performance (although you will have to some minimal coding). I believe there are better ones if you're willing to tinker a bit more.

[0]: https://github.com/snakers4/silero-models