I use one. I prefer spray bars over the standard outlets that come with canisters. If you don't want to buy one ($11 on ebay is what I paid), you can DIY one pretty cheap with pvc
and a drill bit. I can't think of any downside, unless you have fish that like the current (rainbows come to mind). They can increase surface agiation, if that's something that's needed.
"What, exactly, is the internet? Basically it is a global network exchanging digitized data in such a way that any computer, anywhere, that is equipped with a device called a 'modem', can make a noise like a duck choking on a kazoo." - Dave Barry