I realize there are threads already out about the Fossa Tana Pro, but I am looking to purchase one, and I was wondering if, compared to the Grip-B15 there was a major gap in quality. I know there is a large price gap, but that's not the biggest issue. I'm also wondering why the fossa bags don't have the reputation that grip does. This is my first backpack bag purchase, so any input is welcome. TIA