On the 18-55 it will work fine over 50mm.
Under that and it will vignette.
The Raynox is a great piece of kit for the price. As said above, it is easier to focus by moving the camera to obtain AF lock.
The good thing as well is if you get a longer lens in the future it will work with that too (providing the thread size is 67mm or less)
I have mine permanently strapped to the 70-200 and it produces some astounding results.