for QT, I would agreed. showers lost a lot of water due to warm temp and heat if not cover. imo, the regular filter works better for QT tank. it's just for a few weeks quarantine. I would stick with convention filter media such as japanese mats or some other submersible media. it's easier to cover the whole thing too.
btw, it take awhile for the media in the showers to kick in unless it's old media from the existing pond. so make sure everything works before put in the new arrivals.
I setup my QT tank with half water from existing pond and half new water. the filter media came from the existing pond as well. it's like instance established QT setup
Steve