Have seen them used in larger steelhead patterns, but not trout flies. Barbule structure is too big for smaller flies, in my mind. Can be used, of course, as a substitute for mallard, whenever you are trying to get a more pronounced barring and darker pattern.

More useful as wings on patterns such as the Sheep's Creek in my mind, or tails/wingcases in flies like the WD40. No reason why you should not experiment of course and if you come up with something post it, because I've got a fair amount of teal I'd like to make use of as well.