Today I finally got around to cutting the notch in my new 14.5 WSM. It is FAR superior to the grommet IMHO. I have the notch in my 18.5" WSM and my Mini-Joe Gold so have some experience using it.
This time I used an angle grinder with a 1/4" grinding wheel to make the notch. Then, I cleaned up the burrs with a metal cutting file so that the notch would be "friendly" to my probe wires.