I think it all depends on what you have going on. A refugium should stand without fish, crabs, shrimp... if your goal for it is to supply the mt with a source of pods and the like. Sumps and fuges can get real nasty and need regular syphoning of detritus. I find a small dedicated shop vac very useful for sump cleaning. I'm on the fence about keeping a fuge bare bottom or dsb, I don't think a shallow sandbed is that good of an idea. Right now I have a dsb in my fuge; I still vacuum it monthly. It is full of spaghetti worms, the small reproducing nassarius snails might be a good critter too. Having a bb fuge is a sure way your cleanings are getting rid of all the detritus, but I'm not sure if its the best in the way of adding diversity to the system. But solely from a nutrient control point of view a bb fuge/sump is the way to go. I would never buy anything for a mechanical sump, but if something required exile there, I don't see any reason why it couldn't go in there.