I have 3 hermit crabs, 2 turbo snails and 1 cleaner shrimp.
Hermit crab are efficient cleaner. They will eat up left over food and dead fishes but they are also very active. They will move rocks if rock are not place securely and step over corals plus disturb anemone if it is place on the sand bed.
The turbo snails are not bad but they are slow cleaners.
As for the cleaner shrimp, I don't really see it working. I think
it is doing more important task like eating parasites from sick fishes.
I am going to shift my crabs to a small tank and buy a algae eater to replace them. Saw the algae eater working at the LFS. Wow, you must see how it work, fantastic.