One issue I've noticed is that the captive portal works a bit weirdly when you're using AP and station together.
So, for example, I connect to the AP and am redirected to "smart.relay.com" and configure my wifi. It gets given 192.168.1.246 for example.
I then try and connect to that IP directly on my home wifi and it redirects me to "smart.relay.com" again, which obviously isn't a real site. If I turn off captive portal then instead of the redirect I get a 400. I think on the station side of things I should be able to access it using the IP as it won't even have a hostname set up?
I'll continue to play around today, thanks for the hard work from all contributors though!