After it sets saw the the tube in two between each holder. Your holders now have nice wide flat surfaces. Usually you can get the cardboard removed by just pulling. I have never worried about how these look. They usually gum up long before the mount breaks down.
Holders can be anything.
These were the ones advertised to help one quit in 30 days. I discarded the filters but kept the holders. I've even used pipe. I've always used mouthpieces that were designed to be mouthpieces. Either I cut them off of the holder or bought them.