I know that they're increasing in prevalence since others have found them valuable in combatting Dinos....not as common as UV, but a good idea nonetheless.
I bought a tank and it came with one and a bunch of other stuff extra and was thinking of selling it as Im going in a different direction with the hobby so I will never use it.
I checked ebay and WOW I didnt know they were worth that much
One uses a diatom filter regularly in freshwater or saltwater. Once you use one you find out why. One of those things young hobbyist have never learned and an I wish they did as it is a fantastic tool in an aquarist tool box.