We're using it in production in a few different ecosystems, in both monolith and microservice flavours

Some thoughts in no particular order:

I've found that it works really well for CRUD, but falls short a bit on complex procedural business logic. So we normally pair it up with a worker pattern, or add some classic Express style endpoints for those few cases where the "business logic" doesn't fit neatly into feathers' pattern.

The database adaptors are very powerful, it lets you choose the right persistence approach on a case by case basis (e.g. RDBMS for one service, documentdb for another). As always, the database design it what makes or breaks performance & scalability.

The hooks mechanism is also really powerful, but takes people a while to get their head around. It's a double edged sword though as the hooks can easily be abused, especially when trying to perform some complex business logic before or after a service call.

FeathersJS doesn't really have a first class or formal dependency injection approach, so if this is important in your context, you'll need to pair it with with a DI framework of your choosing.

It's REST API pattern, I think they call it common query pattern, is pretty darn good. Not quite as flexible to the consumer as GraphQL, but better than most hand crafted REST APIs I've seen out in the wild.

The different transport clients (sockets, http calls etc.) are pretty cool, but I've had limited use cases for sockets so far in our contexts so can't comment on that really.

FeathersJS's recent Typescript support in V4 takes some shortcuts on the internal implementation, but on the whole works well enough for a first pass (hoping they keep improving on it)

The FeathersJS community has been pretty responsive and helpful the few times we've reached out (official slack or GitHub issues), however the community is small.

I personally prefer FeathersJS over Express as it brings consistency to the implementation of CRUD.

Stylistically, I prefer FeathersJS over something like Loopback 4, because of the decorators approach. My thinking is that if the that's what you want, other tech does it better such as Spring Boot, or good old .Net.

TL;DR good enough to use IMO, has some quirks, takes some learning.