Where do you live? State is all.
I buy Mazuri from a Purina dealer. I feel 21% is too high, and have personally seen effects in my own colony from too high of protein or fats. Males tend to suffer from too high of protein, where nursing females and growing rats will do better.
I would shoot for 16-18%. Although I have to say, I am completely against feeding rats hog feed. Hog feed for hogs, cat food for cats, rat food for rats.
There is a difference in ingredients, minerals, vitamins, and percentages that all take a toll on rats in different ways. Many feeder breeders either don't want to acknowledge poor rats, or just have never seen what a bright healthy rat looks like. I will push anyone I can into feeding their rats rat food. Just how I feel about it. I won't change my tune.
The only exception to that rule is when mixing a diet using a base of lab blocks, and supplement some senior dog food, along with adding in different grains and greens. This is usually going to cost a lot more than just buying a bag of lab block.
I know some people just cant find or afford regular lab block, so they buy cheap dog food. Cheap gives you cheap in my opinion. Any mid grade dog food is going to cost the same as the rat food, so might as well buy the rat food eh?
Any Purina dealer should be able to order the 50 lb bags from Mazuri, and if they don't even try, then I would push them to find out. The price has gone up a little, but 24$ for 50 lbs is ok by me. I buy from a local pet and feed store that deal Purina.
Having peace of mind when feeding my snakes the best feeders is worth it to me.