I love my Ghillie, when I was looking into getting it, from what I saw the Ghillie and the kelly kettles are made in the same factory. The reason I went for the ghillie is the whistle, as I heard the cork was rubbish for holding water in the KK. While its fairly obvious when it has boiled, it is nice to have the sound of the whistle (retro?), also its a extra precaution to make sure it does not run dry. They are very solid bits of kit, about the only way to break them is to boil them dry.
Mine is very much just for brews, fun with the kids and marshmallows, I don't use it for cooking.
If you are not sure what to get, try to get to an event to see some up close.