I bought that Timbuk 2 seat bag from TE. It's a great design (actually it was recalled because the design infringes on Topeak's patent)..However, the spot where the mounting bracket connects to the bag snapped after only about a month of use! The mounting bracket is metal, but the connection from the bracket to the bracket that is enclosed into the lid of the bag is plastic and this snapped. It was on my commuting bike, so I wasn't doing riding that was especially rough. I haven't been able to figure out a way to fix it yet. So that's my experience with that particular seat bag...