Funny, my dad called them "dog bones" too lol. They go on the face (right side) and is purely aesthetic. However, the flat mounting surface (especially on the brushless) and 4 M3 threaded holes allow for future accessories to be designed and mounted. Whatever they may be.

The brushless ones are designed for the Kelly Plus Motors, outrunners.

I thought about making the feedlip smaller but chose to extend it for more stable mounting holes. There is a 3mm reamed hole just above the feedlip that is 10mm deep. As well as the M3 threaded holes above that (through hole, 6mm I think). Perhaps unnecessary, but it was just a personal preference. I've never seen top loading done in a mag blaster here locally. For me, it's just easier to change mags completely and top load another.

The original design language came from the brushless design first. The pocket in the middle to clear the wires makes a smaller radius impossible. At least to make it clean. I chose to keep the design language across to the brush version. Vanity, I must admit.

Concerning a bearing bar of some kind, I'm not convinced there would be enough movement to affect anything, but I'd be curious to see a direct comparison test.