At least with the 5DIII, the RSS L-bracket actually makes the grip more comfortable than without the bracket. Attach one of the little clamps to the side part of the bracket, and you've got the perfect setup -- comfortable in either orientation without anything getting in your way, yet entirely secure.
Going the other direction, pop off the grip (and you can leave the bracket attached to the grip when you do so), screw the BR wrist strap into the tripod mount, and slap on the Shorty McForty, and you've got the ultimate (slightly oversized) P&S.
It's actually kinda scary how versatile the 5DIII is. There are a few cameras that do certain things slightly (but not much) better, but there literally isn't anything it doesn't do well. And pick anything that one of those other cameras beats the 5DIII at and there'll be something else that the 5DIII beats it at. That even carries through to the 1DX -- the 5DIII has silent shooting and can do small and diminutive (no grip + Shorty McForty), and nothing other than the 1DX (and 1DIV?) beat the 5DIII at action.
Totally off-topic, but I do believe that the 5DIII may be the single best camera ever made.