I have a 1" GHD and I love it! I have very thick, frizzy, kinky hair, and it works great on it - better than my comparative Paul Mitchell Smoothing Iron. It was a close contest, but the GHD didn't pull and break my hair nearly as much as the Paul Mitchell Smoothing Iron. I've compared the two even recently, to be sure I was remembering it right, and the results are still the same - GHD wins, hands down!
Even though I have a lot of thick hair, I still prefer the 1", because I can get closer to my scalp in the front. It can handle a surprising amount of hair for a 1" iron!
PS - I got mine for under $100 on Ebay, if you're willing to take the risk.