Been using it for about five years now. I absolutely love it. But I will say some of these comments make it sound like it’s a little easier than it is. I’d say about 80% of your knowledge from Android will transfer over and just work. But the last 20% is a bit of a learning curve, and will take at least a few weeks to get the hang of.
What I recommended to some of my friends that switched is to get the phone and mess around with it for a few weeks before you switch your sim. Then you’ll get the hang of things like alternative app stores and sandboxed play services, and you’ll figure out what you can and can’t do.
I will say the vast majority of things do work easily because of protection compatibility mode and sandboxed play services. But there will be some things that are just more hassle then they’re worth. I find keeping a second device, like a tablet, without a custom ROM makes that stuff easier.
And there are some things that seem impossible to get working properly, at least for me. For example, casting to a TV is basically impossible from what I can tell. Also, tap to pay, even for things like tickets doesn’t work (although if you have play services, you can use Google wallet for things with barcodes).
Overall, it’s totally worth trying out. Just don’t set your expectations too high. You’re not getting a completely “just works” experience.
As for other custom ROMs, I’ve tried CalyxOS and LineageOS for MicroG. I didn’t find either of them quite as good, but that was many years ago. Maybe they’ve gotten better.
Correct me if I’m wrong, but didn’t Prusa specifically say you don’t need to keep the CORE One doesn’t need to be open because of its temperature control?