All I can say is what I have seen here with it going off. It may disrupt the updraft that carries drops of water up into colder air to form hail. I remember them telling me it was good for approx. 80 acres in a radius around it, but at a 1/2 to 3/4 away here, never seen anything bigger than ice chips, or an occasional pea size in the mix.
Several years ago, we had a lot of hail in a storm. 3 miles to the South it destroyed roofs on 1–2-year old houses, and broke vinyl siding on them too. Here with the cannon going off, it looked like you shoveled crushed ice in the yard. Maybe just a fluke, but I feel a little more comfortable when it's set off. My early warning system too, to head for the house.