I have one (not for a glock). There is some benefit in using it, at least to help get your sights back on target after a shot and better practice for reloads, but it is absolutely not the same as live fire. The recoil changes as you shoot and the gas depletes - at first it's more than what I feel with my ammo, then around the same, then way less.
Just set your expectations for what it is and isn't.