The mission bag isn't that large... barely carry-on size:
The thing I like is that you can fold / roll it flat, and it is padded (so laptops aren't destroyed in such a soft bag and it retains it's structure when fairly empty), and it has pockets for keys, passport, etc.
Neat system though the Mission bag is actually bigger than I'd ever travel with, I guess wheeled bags are the real mark of adulthood.