How about grabbing The Sleeve and hiding just behind the door... and when shooter enters, conk him over the head with it?!?
Multi-purpose/multi-task .... works for me in the right circumstances. That being said .....
Seriously, one of the professors at VT was shot & killed trying to hold the door closed against the shooter while his students were all going out windows at the back of the classroom. I believe other students were shot through the door in another classroom while holding it closed. Something like The Sleeve should be standard issue in any classroom with an arm closer, IMO.
I have a close relative who but for their class schedule that day would have been in the building for sure & perhaps a classroom where the shootings took place at VT on another day of the week. This is a deadly serious issue to me.