Delta has had this for around 6 months already. I was never asked to show proof I filled out the form before boarding. I doubt United will delay their flights for this.
The paper forms were basically honor system. There were times I forgot to give to crew and no one cared.
I’ve always wondered who in HNL actually looks at the papers, how long the papers are stored, and if they ever publish statistics based on the data. I think I know the answer.