I say for adult's only because these come out thick and hard, and require adult teeth to chew them down.
Chicken Gizzards are a great muscle meat when served raw. Check out nutritiondata.com for the nutrient breakdown.
I thought it would be a great treat for the puppy (who is teething) but he couldn't get through the raw form. It is really elastic and chewy, and he had a tough time.
So, I sliced them in half, put them on a tin covered baking tray on broil and let them sizzle for about 45 minutes.
They came out looking a bit like chewy beef jerky:
My adult dogs LOVE them, but still the puppy had a tough time with them! He did manage to "num" it down a bit, just chewing it and chewing it. I think it did the trick and he ended up eating two in one sitting.
In retrospect, I think sticking with the raw version would have been easier on us all!