As far as the leave it command, if the poison birds were as far off line as in the video there's not much need for a leave it command and I too would train the dog without that command. However in American AA stakes the line to the blind is down wind and only off line a few yards. I hear the command used often in the field trial world. I like to teach the leave it command while I'm force fetching/hold. I use "leave it" when I take the dummy. This does translate over to the poison bird blind or secondary selection over time if done properly. So Bon, rest assured the command is still alive and well!
On a second note, the water portion of that video, if the handler were to use NO VERBAL BACKS, just silent angle backs, do you all think he would get better direction change and possibly do that blind with half the whistles? Or not?