I see valid concerns on the part of the officer for his safety, but the man who
informs the officer and is legally carrying concealed is probably not the one he has to worry about.
Having the gun clear the holster just makes things far more complicated. I can shoot someone far faster when my gun is in my hand and pointed away than when I have to draw it and then aim, so he's not buying himself much safety. And what if the suspect relinquishes his main gun and use his BUG to kill the officer who thinks he is dealing with an unarmed suspect? The practice of taking the suspects gun only makes sense if the suspect is not legally carrying or is displaying an intent to become violent and/or use the gun.