Only allowed as a cane, not as a seat.
They are tippy, or can be. If it's being used as a seat in a line, someone bumping into it could knock it over. I read a post from someone who was using one in line to sit, got bumped and broke her elbow.
Another person posted that she saw someone using one while waiting for the parade on Main Street. The person was in an area with curb, got bumped and fell off the curb into the street. The person who saw it didn't know anything else about the situation, so didn't know about injury.
Rollators (walkers with wheels and a fold down seat) are allowed and are a much safer choice