Now that the temps. are getting cooler, I am thinking about getting some scratch for the chickens. My problem is, I don't know what kind to get! Is there really a difference in the different brands that are available? I've seen what the Purina scratch looks like, but haven't ever seen any others. Are there brands that are better than other brands for the chickens? I realize scratch is basically chicken junk food, I just want to make sure I know what I'm buying. Thanks!