We use it internally at the company I work for. I wouldn't say it's a bad product, but I wouldn't say it's a good product either.
We've logged countless UX regression issues on their issue tracker and each one has taken 9 - 12 months to fix. Meanwhile, they keep churning out new features that we don't use.
I wish they'd just stop adding new features and spend 6 months fixing their UX and improving stability + performance.
I've been extending and updating the framework for a few years now. There's a tiny userbase but I like writing my games with it.