It was the only grain-free food that the rescue provided, so we have used it for fosters.
In our experience it was a good food. Seamus had severe grain allergies. At first he was on the fish formula but it made him smell fishy and I couldn't stand it because I was pregnant. The duck and potato formula took care of that problem though, and it worked really really well for him. The sores on his skin healed up and everything.
One thing I like about it as an allergy food is that they supplement it with carnitine, taurine, etc. that dogs normally get from a variety of protein sources. Since the protein sources are limited in allergy food, they don't get as many of those amino acids. It doesn't sound like a big deal, but a diet lacking in those amino acids, especially in large breed puppies, has been connected to serious heart problems/heart damage.
If I had a dog with allergies, I'd definitely consider putting them on it. It's a decent food. My only problem with it is the price. The biggest bags usually come out to about $2.00 a lb. which is really high. You can get some of the really premium brands with human grade ingredients and whatnot for less than that. For your dollar it's maybe not as good of a deal as other foods.