It seems pretty much right on topic to me. There is nothing else supporting the saddlebag. This is how Carradice saddlebags were originally designed to be used, many times they would simply rest on the mudguard/fender. Then Carradice introduced the various support racks like the Bagman for bikes with less clearance and also various "lowsaddle" saddlebag versions. I ride a 56 cm bike and the Carradice Camper has a couple of centimeters clearance from the back tire, so it's tight. Mounting without any other support will only work on a fairly large bike. Things like the Bagman have had issues because they do cantilever the load out from the saddle and there are stories of them failing.