I recently crossed the border with my waiver for the first time and despite all my anxieties, it was super chill. I have a drug trafficking charge from around 2002. I was granted a 1-year waiver in November. Leading up to the crossing my brain was thinking of all these reasons it somehow wouldn't work.
I traveled with my wife and kids and we arrived at the airport (Vancouver - YVR) about 3 hours before the flight in case it was busy. We walked up to the guard and I presented my passport with the waiver folded up. He looked at all our passports, glanced at the waiver, and off we went. No secondary inspection or anything took less than 2 minutes. The only question we were asked is how long we were traveling for.
10/10 would recommend getting one of these pieces of paper!