I had two MSR bottles mounted on the side cases of an R1200R. While crossing back into the US at the White Pass portal the US border agent asked me why I was carrying two fire extinguishers. She became embarrassed and grumpy when I told her what they were.
When I consider carrying a fire extinguisher I decided not to, the extra weight and space doesn't warrant the rare chance that I may need to use it.
On the other hand if I am on the trail in bfe and my bike goes up in flames I may wish I had one to save me the walk out.