Quick update - I'm 1-1/2 years on my cabin filter and going strong. When I checked it at the 1 year mark it had discolored but was no where near due for replacement. Although I don't do a lot of gravel road driving, my truck parks on a gravel lot right beside the terminal office for the largest trucking company in our province who also has a gravel lot. We have enough dust to qualify for a desert.
I still believe this is my favorite mod.