I've used it for three years now, both bottom muck and water column. Think of it as just a supercharge...and if you have the muck and nutrients...then you're ahead of the game. Last fall, 2 1/2 years, I mucked the pond with a trash pump and got only a black viscous mess...no leaves or other obvious matter. Think of that with respect to the claims of removing inches of muck...it turns all the accumulating plant debris into black mud...not exactly my idea of a beach. This is a 1/10 acre pond in warm south Texas with large live oaks (dropping a portion of leaves both fall and spring) overhanging. It is bottom aerated, partially filtered (a medium size sand filter), and also circulated by pumps. The fed fish (bream and catfish) took off like rockets and I soon had a heavy load...thinking fish poop. I started adding the bacteria and enzyme treatments...with, I think, satisfactory results. I also use pond dye and occasional shots of flocculant for clearing the water. Lucky me! With only 1/10 acre, my maintenance cost is about $400 per year...all chemicals (including some algaecides) included.
Keep in mind, these are all aerobic bacteria, the muck eaters can't live in and eat under anaerobic conditions. But otherwise it makes sense that a big dose of extra bacteria under good conditions would speed up the decomposition. The theory (a proven fact) is that nutrients consumed by aerobic bacteria are converted to more bacteria (which will die...never thought of that before!) which will respire non-toxic carbon dioxide gas. There is the detritus which gathers on the pond bottom...the non-solvent minerals that were entrained in the tree leaves falling that were consumed by bacteria that died.