Why do you think this would be difficult to do using openwrt? Wouldn't you just set up the travel router to have the same ssid and password as your home network and configure a wireguard tunnel from the travel router to your home network (that is if you want to be in your home network)
Because manually configuring wireguard tunnels on random devices is a simple task for most people lol. Unifi’s whole stack is all about making powerful tools easier to use for people who don’t want to fuck around with networking.