I've been wanting spin pins for forever, but as soon as I saw them at Target I was disappointed. $7?? For two large twisted bobby pins? Come on. So I debated, I picked them up and put them back many a time, until I finally just bought them.
My mother has had success with them and I have been loving my modern updo pin so I decided to go ahead and get them.
So glad I did! These pins are my new favorite toy! They hold my hair very well, and keep the shape of a bun much better than a hair tie and bobby pins do (in my hair at least).
Kind of hard to explain how it works with words, but basically you make a bun out of your hair and spin the pins in clockwise at the base of the bun, from opposite sides (my favorite part of the tool is how easily it comes out, all it takes is a few counter-clockwise spins and it's free).
For a better visualization, this video includes the spin pin until 0:25 seconds.