My needs are very simple - can I start using CI4?

Nice! That makes me happy to hear that. I'm curious what edge cases we helped solve, though?

Other than the entity, using UTC timestamps, etc, which are more common, the one thing that I can remember making me go "oooh, didn't realise someone else needed that" without browsing through documentation is running multiple applications with one CodeIgniter installation.

Assuming there's a way have shared models/libraries somewhere all apps can access, it just looks much tidier solution coming out of the box with documentation than what I had hacked in.