HACS installs community integrations whereas addons are like external programs that hook in HA. You can do the same thing with HA in Docker by installing the addon containers separately and then hooking them in manually but HA OS makes it much simpler.
For example I’m running the Mosquitto broker, Z2M, a Visual Studio Code server, diyhue, and Music Assistant as addons.
Docco page about it is here: https://www.home-assistant.io/addons/
Good shout. I’ve just recently moved from Pihole to Adguard Home myself, complete with Hagezi lists. I consider myself very tech savvy and I work in the field but AGH suits my needs much better.
One example is wildcard DNS to route all of my hosted services via reverse proxy. In Pihole I had to make weird blocking rules to make this work, but AGH has specific settings for it. It also supports DoH out of the box, whereas Pihole needs non-standard faffery to get it working.
Very pleased with AGH in general.