I had two diamond watchman gobies and they both jumped out of my tank! Make sure you cover your tank or have some kind of egg crate thing.
For the few days I had them, I did like how they sifted my sand.
I also like those nassarius snails but my LFS
never have them in!
I am going to get a couple of brittle stars for my tank too..I heard they are also good working in the sand and eating detritus.