> Also tempted to attach a touchscreen to my raspberry pi, put it in a nice case and use that as a UI for it, though adding a web browser to the installation rules out using HAOS directly I guess?

I don't get that part? HAOS is a Linux distribution with a pre-configured / installed version of Home Assistant. It behaves (almost - see below) like a "normal" Home Assistant installation.

> What are the reasons to prefer HAOS over installing via docker on a host system?

For me it's that you can manage "addons" directly via Home Assistant e.g. if you need a MQTT broker on your system (I do because I use zigbee2mqtt for integration of my Zigbee devices) you can just go to the addon store, click install and it also automatically integrates with Home Assistant. Same for zigbee2mqtt. If you want to do that with a container version of HA you need to start up a MQTT / zigbee2mqtt broker manually (as another container) and then connect it to HA. It's not the end of the world, but why make it harder as it could be.

You can also upgrade HA via the UI and don't have to stop the container, chose another image, restart the container. Backup & restore is also breeze.