The 1.47 mile (18:13 moving time; 12:23/min pace) felt pretty good.
It was also my chance to try out the Airwaav which is supposed to improve breathing by positioning the tongue down and forward. I cannot speak to the performance impact, but I did like the feel of this mouth guard and will use it during Crossfit workouts. It was not particularly snug which is to be expected as it was not in the league of the night guard my dentist made for me.
I understand the criticism and why it would not be suited for powerlifting. It does absolutely nothing to stabilize the jaw, but it does protect the teeth when clenching.