My rangefinder is a Leica 800. Size does matter, this one is with me all the time, though I use it less and less. They are a great learning tool, test yourself and friends all the time, soon you will relie on it less. Now I use it more to settle a disagreement about range.
Foxer - Very true about PBR. Most flat shooters can be zeroed at 300 yds. and get 99% of the shots in the KZ. Just remember the POI at 150 is high. Most hunters like to have their rifles 0'd at 200, so their is no correcting at shorter distances, knowing that this is good for most occasions. Thus the adjustment (holdover) for the rare long shot.
I think alot of the error occurs because lots of hunters don't realize the correct distance in the field (even on 200-300 yd ) Try judging a moose when you can only see 12" of the back, or a buck wwwwaaayyyy across an open cutblock which has as much vertical as horizontal ground. Rangefinders tend to make liers of us all, sometime or another.