Oh and I liked the idea enough to buy one because I am always out with my camera and no camera bag, so carrying around anything else just wasn't happening. I will always have a lens cap with me so it seemed perfect. And with it there "in my face" I am more likely to remember to adjust the WB before I start shooting.
Those were the selling points for me. The downside, you have to have one for each of your lenses if you have more than one (that are different sizes like my 18-55mm and my 50mm). Ok off to try to see the difference LOL!