PG,
I have different philosphy on using the radar gun on younger pitchers than most do. No problem in certain situations, but there are dads who regularly place the gun on their pitcher everytime they throw a pitch.
Good coaches and and perhaps their dads who know their pitchers know when it's time to stop, usually other signs begin to show, walks, change in arm slot, etc. My husband never needed a gun to know when his pitcher was done for the night. Pitch count, longer innings, drop in slot he picked up on that much sooner than later.
Younger pitchers tend to pitch to the gun, that's just my opinion. They tend to over throw and then you get problems.
I think Sully rarely used the gun during bull pen sessions but did in a game, but I don't remember any coach gunning him during games until his last year of HS (that doesn't include showcases, tournies, etc).