The Swing is attached above the shock so only the wheel is bouncing around. The OMM is attached below the shock so I guess the wheel/rack/pannier competes with the rest of the bike to bounce around... Anyway, the latter would seem like it would greatly dampen the relative movement of the shock, resulting in a much rougher (like in no shock) ride.

I used a Swing on the GDMBR and it was fine.