They have their uses on a defensive handgun; mainly when forced to use unconventional shooting positions, such as on your back, shooting over your head...etc.
Fad they ain’t; they are used by very serious, professional shooters, every day.
A good backup to irons, and as noted above they are excellent for non-standard shooting positions.
Or, are you expecting to have time to take a Weaver stance and get a traditional sight picture during a surprise encounter when your life depends on it?
Hans put it best. If you were to find yourself in a shooting situation where you were on the ground or in a one handed situation or needing to fire or aim fast it could or would be beneficial. Nothing wrong with it however I would train with it. Shoot with it one handed and run some drills with it.