That sucks (the bolded part). The one in post 5 looks like a 1/4" toggle, which I wouldn't use... I'd use a 3/8".It was the hangar that failed.
The hole in the ceiling was perfectly fine....the screw stripped.
And it was just a small 6" pot...so even freshly watered, would not have hit 11lbs.
As for screwing into studs.....I would never just use 2 screws...my hangars have 6....the chance of all 'heads' 6 failing is virtually improbable.
(it was the one pictured in post #5)
Yes, all 6 heads failing is unlikely. The OP linked a hanger that has two, and if the top one fails, it'll fall. I had my wall-hanging phase (I keep them in a case now, too), and always used toggles behind the drywall. They kept for the 5 years I had them up. Not a long time by any stretch, but, when using the plastic "anchors", I had one fall within a week.