I was nearly a simul rap casualty in the Potrero a decade ago.
Was practicing with my partner on an easy route we were descending. Neither of us had done it before, but we wanted to do Timewave so it seemed like it might be a good skill.
Got to an anchor, partner got there first. We were talking our way through it, I told my partner to clip in but not to unweight his Grigri. Well, he clips in and automatically hits his grigri handle, so I got to experience a moment of weightlessness before he released it. Seriously thought I was
Going to die for a Second.
Not worth it.