We use it in production and are really happy with it.
For me, one of the biggest value points of Ash lies in removing the boilerplate without locking you in.
The devs of Ash cleverly use Elixir itself and other big names of the Elixir eco system. By doing that, they have created a framework that helps you moving more quickly as you don't have to write the same code over and over again (i.e. remove boilerplate) while still giving you the flexibility to escape if something out of the box doesn't fit right away (that's because of how Elixir works and how they just re-use the other big names, e.g. Ecto, Absinthe,...).
I've tried to write about all of this here if you are interested in reading more:
https://www.lukasender.at/ash-the-hidden-champion-of-low-cod...
In the end, it's hard to only write and read about this. You can only "feel" how things change when you actually work with it.
The learning curve is a little step at first, though (in my opinion). But the docs got a lot better over time.
All in all, I'm still happy with how things turned out and would use it again for future projects.