The effects for me (living in Brussels city centre, so quite noisy - police, ambulance, sometimes loud tourists past midnight, and a bit of construction at 6am nearby to keep it real :-) ) were very pronounced:
From needing 9 hours and feeling groggy in the mornings anyway, to easily going on 7-8, feeling very refreshed and alert each day.
A cool side effect was that this superpower works also while traveling - so, I no longer care how noisy the airco is in the hotel room, being next to the lift, or having the window above the lively bar.
The only downside with those earplugs that they are good maybe for 3-4 nights and then are too squished to be useful; but the upsides more than make it up for me.