Any mixing or feeding I do is by hand, so my mix will be something like x of this feed, then, y of that feed, then, z of that feed. I will try and give the hay before anything too rich....
Anyways, I think, at least with the feeds I get cheap or free, that when buying, I always try and take highest protein with some minerals etc incorporated, because often other feeds are not high protein and mine are still growing.
You need to calculate all feed values, so you know if you have right energy and protein in the mix or total ration.
lets say you can get a real high protein feed for similar price to the 12, you can then have poorer hay, or whatever....that is what I would look for anyways if buying a commercial pellet or feed.