Right, or beside it, or whatever. After having both I think the filtration is superior to the HOB
in many cases, as they seem to really move quite a bit of water. I like them because there is no monster box hanging off the back of the tank, but only a few inobtrusive hoses. I often supplement them with a HOB
with biowheels. You can get a biowheel attachment that connects to the outflow of a canister.