They fit neatly and pretty close to invisibly inside my latest boots, they are comfortable and I used up some of my oldest stash.
I made the medium and, with the benefit of hindsight, could have made the small. But this give my feet plenty of room to move, which is the principle behind "barefoot" shoes.
I'll leave you with a bonus, which reminds me of my school days and gets stuck in my head all the time:
The Black Sock song: