Most fixed cups can be removed with a big crescent wrench, but it definitely helps to have a clamp or a version of the Sheldon Brown tool because the exposed flats of the fixed cup are so thin. The Sheldon tool gives you an extension clamped into the cup itself to give you a better purchase with the wrench. You can also use a longer bolt with bigger washers to keep the wrench snug against the bottom bracket cup, like with the clamp. I would say it makes more sense to spend a few bucks on some version of a clamping device than on the specialized wrench to fit the cup.