Do You Like octaves (played or heard on harmonicas)?
Yes.
Do you play them?
Yes, on octave-tuned instruments.
Do you like to hear others play them?
Yes when the 8vas are in tune. And, in some
cases, when the 8vas are intentionally
de-tuned for a tremolo effect.
Advantages?
Sound re-enforcement; amplification for emphasis.
Disadvantages?
For me, playing 8vas on single reed harmonicas
is difficult; so is 8va splitting.
Do regular folks (audiences, non-players) want to hear them?
Regular folks probably don't know what they are. Ask regular folks.
Best Octaves to You, Stay Healthy
JB