According the data from Phase 3 Pfizer, you can have up to 89% efficacy after 15-21 days from the 1st shot only. That's quite remarkable considering we all get annual flu shots with efficacies ranging in the 30-60% range. Not quite sure why this story's author calls the 2nd dose "crucial", considering the J&J max efficacy for a single dose is in the 60s. I get that they are going along with the phased trials recommendations, but I think the 2nd dose could be a bit overkill in many cases (especially younger people with healthy immune responses).
Regarding symptoms, everyone I know got a headache and fatigue from the 1st Pfizer dose, including me. My brother had a massive headache after the 2nd dose as well.
I, for one, feel comfortable with just 1 dose, but unfortunately I'd be demonized as a non-completer.