I also have that hat. It is nice that it rolls up (just kept it clipped to the backpack most of the time) but my biggest reason for purchasing it was the open top. We were doing our first August Disney trip and in that kind of heat and humidity I knew I was going to want to wear my hair up the whole time. This hat could go on and off without messing up my hair.
I didn't wind up wearing it much, but it was nice for the few times you're stuck waiting in the direct sun. It's also great for the beach or pool.