At first, many students were nervous about filming themselves, and they didn't like hearing their recorded voices, but after a number of tries, they've become more comfortable with it.
In English 12, we're reading The Curious Incident of the Dog in the Night-Time, by Mark Haddon. The main character and narrator, Christopher Boone, has Asperger's Syndrome, and throughout the narrative he demonstrates and reflects on how his mind works.
I posted this assignment for my 1A class: "Chris says his memory works like a recording device. Use a different simile to describe how some aspect (memory, thought-process, imagination) of your mind functions. Be specific!" You can see and listen to their responses here.
Most of them managed to find interesting ways to describe the workings of their minds, and they've learned to think ahead about what they want to say. Some of them are (somewhat obviously) reading from a script they've written, and that's okay. They were also quite specific and provided good examples, which is what I wanted. They packed quite a bit of information into 90 seconds!
One other nice thing about Flipgrid is that it was created at the University of Minnesota!