I'm with you on that Tim.
Seems they either come in or not. No great preference on their part. I always put a few teal dekes off to the side of my spread and have yet to see any teal drop to them. In the past we killed just as many without teal decoys as with.
Interestingly, when using nothing but teal decoys we've killed just as many other birds as with decoys of their kind. A partner of mine has video of about 500 canadas coming in to his teal spread over the course of the morning. Other puddle ducks don't seem to mind coming in, and may actually prefer teal after getting shot at over all the other spreads of mallard decoys.