Do you use special effects filters?

I'm seeing a trend. While you can add special effects in post, it seems like a lot of photographers are "dirtying up" their images with filters lately: motion blur, split diopters, drag filters, etc. I'm talking specifically about the ones that you physically hold in front of the lens (K&F makes several).

Have you used any of those? What was your experience with them? Seems like they would be difficult to shoot with.