You can let regular clients in on the second 5GHz radio if you choose to, and if you're not using it for wireless backhaul from another node there should be no reason not to. As to how well that really works, I've not tried it personally. I've been pretty underwhelmed by the stability of ASUS' firmware in any even-slightly-off-the-beaten-path configuration, so I would not be surprised to hit some issues using it this way. (Now that RMerlin firmware is available for the XT8, it might be worth seeing if that works well.)