A part of the haul. Left to right: tongue, heart, liver, oxtail, and chicken livers.
Organ meats are not only amazingly nutritious (wild or grass-fed/pastured) they also allow you to purchase high quality animal products at a fraction of the price. Some skill is required in cooking these items, but with a good book like The River Cottage Meat Book, you will have no problem. Why eat these items? Don't. There will be more for me.
I kid. It is worth it for the adventure in the kitchen and, worst case, you'll have a quality treat for the dog(s). The tongue requires a bit of work, and the liver may be rough for people with texture issues, but the heart is a muscle and much like meat. Of the above haul, I've not cooked with oxtail, but it is first on my list. All this being said, I cannot stress how important it is you get these items from naturally raised sources. The standard grocery store items, should you be able to find any of them, are woefully substandard. So go, find a farmer, meet the animals, and then eat the animals. All of them, head to tail.