if its in an aquarium full of water, they can and will get nutrients from the water column. its not like its dry in the substrate of an aquarium. if its in the water, its in the substrate.
better than the cup they come in, but no company should be selling bad ideas like that. just shows that when it comes to dollars or integrity, too many opt for dollars.
large... i used to have sturgeon, and even with the tank in the other room, they liked to breach the surface in the middle of the night blowing the lids open on the tank. quite loud and startling the first few times you hear it.