I have Brions and stretch Zions. The Zions have a much looser cut in the thigh. I wear Brions for work in the summer and they are great. Also have rucked in them many times.

Zions have more room but aren't sloppy. Brions are trim but still let you move. I don't like the Zion belt as it always seems to get in the way of my appendix holster. Brion pockets are on the small side.