Zensical team here. It's perfectly usable – we're of course building our own docs with it and the first users have already switched – but you have to have an eye on compatibility. Whether you can switch right now largely depends on which plugins you're using from the MkDocs ecosystem. We have an entire section on compatibility.[1]
If Material for MkDocs ticks off all or most of the boxes, you can definitely start using it, and switch later once everything you need is available. Our promise to the 70k+ projects using Material for MkDocs is that we'll make switching to Zensical as simple as possible with automatic conversion tooling once we ship certain functionality. The compatibility we have now is a first step towards that goal.
If Material for MkDocs ticks off all or most of the boxes, you can definitely start using it, and switch later once everything you need is available. Our promise to the 70k+ projects using Material for MkDocs is that we'll make switching to Zensical as simple as possible with automatic conversion tooling once we ship certain functionality. The compatibility we have now is a first step towards that goal.
[1]: https://zensical.org/compatibility/