Hi Eric,
You are right, I also have a Fritzbox as my main router, and have been doing exactly that until a few weeks ago when I found out about this network isolation option on the Aruba. With the Guest option i could never isolate all the devices as some of them, like a security camera, nvidia shield… needed to remain on the main network. Now when it is 100% isolated I can’t say I hear any sound difference between the 2 options. It just makes me feel good:)
Cheers,
B.