With the increasing interest in pistol ARs, thanks to the ATF ruling on the SIG Brace, the 5.11 Select Carry pack is looking a lot more useable now. I was talking to a School Resource Officer who was contemplating carrying an AR-15 on duty. He was ambivalent due to pros of having one for an active shooter scenario and the cons of having it at all times. If he locks it up in his office, it is useless when he may need it to respond to an emergency. My concern is the open carrying of an AR-15. Even though he is a School Resource Officer, I can just see ignorant people freaking out. Most likely parents.
I recommended looking into a pistol AR, since engagements will probably not be very far. With a pistol AR, it can be concealed and I showed him this video.
Now the video shows an MP5 but you can fit a 7.5″ pistol AR inside.
A 10.5″ pistol AR however will stick out.
Here is what it looks like when worn. If you are clever you could dress up the buffer tube like a tennis racket handle and no one would be the wiser.