I have the B-Bag, and it's a really nice bag for transporting a Brompton, but that's mainly to a hotel where you will leave the bag there. It's well made and beefy, but that's the problem: it's heavy. And while it folds, is doesn't fold very small. You can lash it folded to the rear rack, but it sticks out a lot. I tried to lash it to my backpack, but it's pretty heavy and bulky. Simply put, it's great for transporting a Brompton but you wouldn't want to take it with you somewhere, either on the bike or on your person. And it is expensive. I got mine free since the bike shop screwed up on the color of the Brompton I ordered, so it was cheaper for them to give me a free B-Bag than take the bike back.