This, to me is the most important metric. And from a person who is allergic to absolutely nothing thank spaghetti, I’ve always noticed this aspect of vacuums
To the point where I make an effort to start my vacuum out the door when first starting it such that the initial blow of the fan blasts the dust captured within to the outside.
Most people don’t realize that many vacuums have a small filter for the escape air and they never clean or change that other filter
EDIT: I also, will never have a carpeted home. The reason is, once you have a fully hardwood home, you realize just how much actual detritus accumulates in even the most lightly traveled areas.
In the 1980s we bought a house in Tahoe, and it had 2" (TWO INCH LONG) shag carpet. and it was RAINBOW COLORED.
I wish I had a pic of it, but it was literally 2" long rainbow shag carpet that was a nightmare.
https://i.imgur.com/u4sFJj2.jpg
But the entire house. 1982 cocaine house.
Carpets were invented to hide dirt. The history of the vacuum is quite amazing.