I can think of one situation I have right now... The M1 with the 2 to 4 point mount, I wouldn't have to use the brake bridge mount. I have a frame right now I would like a lower rack on but I can't get the bridge mount between the fender and side pull caliper or between the caliper and the headset cup. It is just that tight. So for right now I am stuck with a bar mount till I figure out a solution. The M1 might do it if it could fit on the middle fork braze ins. If you don't forsee sidepulls on your bike, I don't think you will miss the M1.
What I would want is a rack like the Velo Orange Constructeur rack with drop out mounts and a rear mount point of the M1 so I could be sure it wouldn't drop onto the wheel and still avoid the brake bridge mount.