aellman Loc: Boston MA

The claim about a lens hood having any effect on window glare is highly suspect, i.e. impossible.

E.L.. Shapiro Loc: Ottawa, Ontario Canada

It does not eliminate or reduce reflections when shooting through glass- that is the job of a polarizing filter. It does, however, prevent light from the side from striking the glass and thereby causing glare, that is, providing the circumference of the Ultimate Lens Shade is flush with the glass surface. The shade is acting as a surrounding gobo or tent. The same effect can be had if the lens is flush against the glass but you would be unable to slightly tilt the camera to compose the view you want to encompass. In an aquarium, you could damage the glass without using this as a buffer.

So...just think of it as on onboard portable tent and a handy super-sized shade when you need one. They are not terribly expensive and they do come in handy.