I like the Dokkens and the dogs like them. The Avery's are like blown up footballs at first I thought they would be great but found out in less than a year they were not going to last. I have had Dokkens for years the avery's I bought lasted a little while then cracked and the dogs really didn't like them. My Dokkens I use when I can't use birds. Young dogs and puppies love the Dokkens for some reason. It seems expensive but I use Dokken of different size and have had some over ten years and trained a bunch of dogs and they still look pretty good. I have broke a head on a Dokken when it landed on a rock but normal use not a problem.
I've had both and prefer the Dokkens. My dogs do not like the Avery's and they do crack when cold. I have had heads crack with the Dokkens but that is about it.
I think the Dokkens suck overall. The foam breaks down, soaks up water, they become heavy when saturated, and if used regualarly they never dry out. The heads will crack, and they stink - BADLY! Other than that, they're just great. The only thing that I do like about them, is that the foam soaks up bird scents easily, which makes them usable for teaching tracking.
I've never seen an Avery crack - but then I'm not in an extreme cold climate.