These checkpoints are pretty common in PA, I've only ever been stopped at one and that was a "seat belt" checkpoint. More common is the DUI checkpoints at night they set up they occasionally on the weekend. Never went through one of them. I have been stopped numerous times in the truck by DOT but that's a little different and understandable IMO.
Frankly they should be banned as unconstitutional, the argument is that driving is privilege and not a right. At the very least if it's a "seat belt" or DUI checkpoint that's what they should be looking for and send you on your way if you have your seat belt on or they have no suspicion you are intoxicated.
As for the cop going for the gun I don't blame her, if I was an officer of the law my hand would be on that pistol when approaching any vehicle.
Edit: good topic, I changed the title.