Sponge Files??

How many people here have used Sponge files?
And what do you think about them?

I have been using them now for a bit and I really like them, saved me buying a lot of sandpaper. They worked well for me both on wet and dry sanding.

I tend to buy bigger sheets and than cut them to a smaller size at home.
The other material I use is cloth backed sandpaper, more flexible.