Yes, I have a bike with a Brooks Champion Flyer that has a Bagman mounted to the lower set of saddle rails along with a Carradice Barley bag hanging from the bag loops. It works just fine and I've had it loaded with lots of heavy cargo from time to time. If you stop and think about it, the Bagman is fastened to the lower "fixed" set of rails while the bag hangs from the loops on the rear saddle frame that sits on top of the springs. So when you go bouncing over bumps and the springs compress, the load in the saddle bag (that sits on the Bagman frame) simply stays in one place. And yes, having the Bagman does make a big difference in the vertical positioning of those pockets.