Not sure how well that would work to be honest. In theory it sounds good, but in practise, if were going to an incident 'at pace' , it might end up banging against the back repeatedly as you walk/jog/run to the incident, plus if you do trip you're going to have the extra weight of the extinguisher on top of you. They aren't the lightest of things to carry
I could be wrong of course, might be great !