I love them. They also fit under the machine (if I want to machine bind) and they slip around on the fabric easily if you need to move them, or they stay put.
I used to use the dritz (?) brand binder clips, but those are so hard to fiddle with since they are the big spring type and don't slide out of the way very easily.
I only use the office supply binder clips to keep sections together (per suggestion from Judy Neimeyer - I took a class from her).