I just bought the same hair dryer. I'll be in England for 2 weeks this summer, so I needed one with the international switch.
I've only used it once, and can tell I'll need to get used to it. I'm considering buying another of the one I have currently, though, since its not an expensive unit either, and because I'm so used to it! (It's a Revlon dryer for about $17)
I have always diffused with the cool setting! I'll start out warm and on low, then I go up to high on cool. Warm and high are for when I'm in a hurry or my hair is particularly "wet" or "heavy" feeling. I love it! I'll never buy a hair dryer without a cool setting ever again!