In reply to Wiley Coyote:
That's exactly my concern with the Grigri and is why I'm not a big fan (though I do have one).
But one thing that does surprise me is the way people cite weight difference as a reason for using a locking device. Surely that's a reason to consider weight bags, ground anchors and the likes if they'd be pulled up dangerously so they might start lifting gear out / hitting the first clip?
Or is it more about "what if they are slammed into the wall"? If so, weight bags/ground anchors can help avoid that, as can the belayer standing in a sensible place reasonably close to the wall. After all, I'm 18st and much smaller people have lifted me off the floor when taking a big lead fall.
After all, being big and heavy does not necessarily mean you're going to be more attentive nor to have a tighter grip on the rope when using an ATC or similar. Yes, the forces are a bit greater, but it doesn't seem to make all that much of a difference in terms of the plate's ability to lock off, assuming you aren't using tiny ropes.
Neil