Thanks for that link.
. Lots of great info there.
The under seat limits are 45 linear inches for the airlines I frequent. I don't mind some protrusion during take off and landing. 9X14X22 is what Delta lists as their maximum under seat dimension. I prefer window seats, so the long and skinny profile seems a good "fit".
I do like the Briggs-Riley products but have some non-air-travel uses planned for which I feel the Red Oxx is more suitable.