Raw 100% grassfed and wild suet (aka perinephric fat--it's called that because it's the fat that surrounds the kidneys) has provided me with more benefits than any other food I've tried up to this point. I prefer it to 100% grassfed marrow, though I eat that too, and the suet is cheaper, especially if you don't consider the bone part of marrow bones to be equally as valuable as the marrow itself. I haven't tried back fat yet.
As an experiment, I stored 100% grassfed suet in a paper bag in the kitchen cupboard for over a year and it didn't spoil. It did absorb some of the taste of the bag, though, and it tastes best when fresh, of course (though not straight out of plastic--when I buy some that's wrapped in plastic, I air it out before eating any). Suet stored in the fridge in plastic bags/wrap becomes coated in moisture and spoils rapidly.
Most of the 100% grassfed suet chunks from a reputable farm that I buy at a high quality market have little or no brown bits in them and very little connective tissue. I choose the ones that are the purest fat. Wild suet has been even better--pure hard fat with no observable brown bits or connective tissue.
When I first started eating raw suet, my system was not yet well adapted to digesting fat and some of it went through me--especially the grain-fed supermarket suet--but now it digests well and I no longer see any sign of it in my stools.
