Lots of good info here.
I counted up and have or have had 10 single speeds...almost all cheap finds, mostly around 67 gear inches eg. 42/17.
A few have been given to grand kids to ride down to the lake, and a couple flipped.
I rode all of them, at least briefly.
The greatest surprise to me has been that they are nearly as fast as multi-speeds on most roads, maybe two minutes slower over an hour.
All climbs are out of saddle, all steep descents are coasting, long upgrades a hammer, long slight downgrades...the one real disadvantage.
I know, everyone's different.