I've used it in a couple of small Android apps. Overall, I wouldn't recommend it (yet) for anything more than toy projects. The sibling post mentioned a few reasons why, but here's are another few:

No inheritance. No nested transactions. No RxJava support (due to threading issues with Realm). Many annoying random errors (for example, get a row then close the DB connection -> You can't use those results after. Although I believe that this is by design because Realm doesn't cache any data - it queries every time it's requested AFAIK).

It's definitely on the way to being an awesome asset, but it's not there yet!