I thought the site I found said that only Fermcap S must be filtered, Fermcap AT does not. No real distinction on your link.
I only use it in starters, but that makes me wonder. Good old paying attention works for the kettle.
I had heard that also, so I bought some AT. But I've come around to your way of thinking...I use a little for starters, but I'm back to using a spray bottle for the kettle.