Just came back to post an update.
A little over a month later, still running perfectly

I saw there are some quite nice little OpenWRT dev boards available for not much money.
It seems that RasPis are rarer than a caveman's steak at the moment though.

For the same price as you will pay for a Pi4 currently I went for the virtualised approach shown here - https://www.servethehome.com/topton-intel-j4125-4x-i...

I can likely run a number of small appliances in this way such as Pihole and a Unifi mgt instance.

Yeah, I liked the idea of an x86 based solution, but couldn't find a reasonably priced option that I liked. Given I already had the Pi4 sitting there I only needed the extra USB network adapter. I could probably sell the Pi4 for a profit now 😄