I don't have an answer for your question, but have totally hated UI's direction for my use case and business. Do I still buy their APs and switches? Yes...do I wish there was a better alternative, ABSOLUTELY.

I've tried Omada and the interface seems clunky. I wish there was a self-hosted, open source alternative to the Unifi Controller that would allow us to remotely manage self-built or openly programmable hardware.

I'm curious to see what others use, but I've been using Uptime Kuma for this purpose at several different sites I manage. I run Uptime Kuma on a VPS and locally on site. I have the local instance monitoring the router, gateway, DNS, and several other internal and external devices. I also have the local instance do a "push" check-in on my VPS instance. This gives me a pretty holistic view of things.

Probably closer to $0.25 check so lawyers can get their well deserved cut.