The ruler is tremendously handy. They have lines so if you want you can take them out and use them as a ruler.

These are the best ever. They are also great for use as a ruler and for drawing various shapes using the edges. These are actually rather handy.

They are thin enough to still be unobtrusive and flexible. The thickness is a good development, these are not flimsy. They are durable, easy to use, stay in place and can be written on with pencil and then erased.

Only thing that bothers me is that they get tangled up with each other with the ring. They stay in place by a tiny sliver of plastic.

Plastic snaps easily into spiral notebooks. Practical and multi-functional. I use them in my homeschool curriculum books.

This just falls out of my planner. It's not securely attached at all. Also refuses to return my purchase even though the listing says it is returnable.