Of course it all depends on which bits of the Unifi ecosystem you are using. If you just want a singular device like a firewall or a WiFi AP, you can find alternatives.
But for the full stack from firewall to switches to APs, there just isn't anything that integrates as well as Unifi gear.
https://www.lannerinc.com/products/network-appliances/x86-de...
One must install the OS; whether that is OpenWRT, OpenBSD or whatever OS. This means that one needs to be quite familiar with the OS install. So, one probably needs to be a technical person. The one I got had x64 intel based CPU, so it should run just about any linux or BSD distribution. The one that I got has a serial port for the console (no VGA, HDMI, display port etc).
I suppose some people might find their use of a cloud based "controller" disagreeable, but I honestly think it's a plus — it's barely ever needed and it's one thing less to maintain.
Until your network gets pwned because the cloud controller gets breached.