I've done a product evaluation of several possible feeds to use at the barn: CPI Equi-Balancer - not really a feed as it's a protein/mineral/vitamin balancer pellet (from CPI, now called Landmark, in Wisconsin - I drive up there and pick it up), and Buckeye Safe 'n Easy (pellet, not texturized) and Nutrena Safe Choice (both available from our local feed store). (At the end I also mention Triple Crown Lite and Low Starch.)
Disclaimer: I'm not an equine nutritionist, just an amateur. I know enough to be dangerous - I've tried to learn about the topic and have a general idea of what to look for, but equine nutrition is a complex topic and there are many elements to look at - and you have to look at the whole picture - the whole diet: forage (grass/hay) and feed, the horse's activity level, age and any special factors - HYPP, PSSM, condition of teeth and digestive system, etc. In my analysis, I was looking at a number of factors - cost per serving (in our case the lowest cost per serving turned out to be the best option nutritionally for our group of horses), what the feed is designed by the manufacturer to achieve, levels of protein, fat and fiber, NSC (non-structural carbohydrates) levels, ratios like copper/zinc and calcium/phosphorus ratios (you'll want a different answer on this depending on whether you feed grass or alfalfa hay), selenium levels - a particular issue for our part of the world, and anything else that sticks out. In order to do this analysis, you need to know what recommend amounts of the various components are and then analyze feed labels to see what you've got - and learn how to do the conversions between percentages, ppm and grams or milligrams per pound or kilogram - fortunately, Charisma's owner, who is a close student of nutrition, had already done a lot of this preliminary work for me. We were not looking for a complete feed as our horses get plentiful forage - grass and/or grass hay - but if your horse has limited forage or cannot adequately digest forage (poor teeth or age) your answers would likely be very different. Our horse population ranges in age from 5 to a (lively) 22 and all horses except one are in regular light to moderate work.
All three of the CPI, Buckeye and Nutrena feeds are sold in 50 lb. bags, and the per bag prices are comparable (but as you'll see per bag price doesn't give you the answer due to the per horse per day feeding requirements of the different feeds):
Per bag, including sales tax:
CPI Equi-Balancer: $17.82
Buckeye Safe 'n Easy: $15.95
Nutrena Safe Choice: $15.19
The issue is the amounts of feed needed every day (as recommended by the manufacturers) to get an appropriate daily level of vitamins and minerals. The recommended feeding amount for CPI Equi-Balancer is one pound per day per horse - or a cost of $.36 per day per horse or $10.80 per month per horse.
The recommended feeding amounts for both the Buckeye and the Nutrena for horses that are inactive or in light work is approximately 5 pounds per day per horse, or a cost of $1.60 per day per horse, and $47.85 per month per horse for the Buckeye and $1.52 per day per horse for the Nutrena. That said, both the Buckeye and Nutrena feeds assume that more total calories will be provided by grain and less from hay (they assume 16 and 10 pounds of hay per day, versus the 24 pounds a day the vet hospital calculated for Pie) than the CPI feed does, and both the Buckeye and Nutrena feeds provide significant more calories from fat and protein than a daily serving of CPI does - the CPI feed is designed only as a concentrated vitamin/mineral/protein balancer pellet. (I do not have accurate kcal/serving data but believe it would confirm this, looking at the protein and fat percentages of each of the feeds and using the recommended feeding amounts.)
If you fed the Nutrena and Safe Choice at the recommended amounts per day, you would probably have to reduce your grass/hay feeding to avoid too many calories - but the result of that is that your feed balance would have shifted to more concentrated feeds and away from forage. If you wanted to continue providing the amount of grass/hay we typically feed, you would probably have to feed less per day of either feed in order for your horse to not get too many calories, but the result of this is that, since the vitamin/minerals provided by Nutrena and Safe Choice are significantly lower per pound than the CPI, your horse might not be getting enough of certain minerals and vitamins.
A lot of details - my conclusion is that the CPI Equi-Balancer is a better choice for our horses - it is specially formulated for our selenium-deficient part of the world, does a good job correcting deficiencies in our hay/forage, which we've had analyzed, is lower cost per serving (even if you only fed your horse 2 pounds a day of either the Buckeye or the Nutrena feed - which might provide inadequate vitamins/minerals), and doesn't provide extra calories that many of our horses don't need. From the barn's point of view, if a horse needs supplemental feed to maintain weight in the winter, rice bran or another feed like Buckeye Ultimate Finish, or beet pulp (although it's a pain to prepare in the winter) can be used for weight gain.
That said, both the Buckeye and Nutrena feeds are good feeds with adequate vitamin/minerals at the recommended feeding levels - including appropriate calcium/phosphorus and copper/zinc ratios, and even adequate selenium per day for our area. I have reported NSC (non-structural carbohydrates - the rapidly digested type) levels for both - the Buckeye feed is lower - 12.5% (thank you, Buckeye, for putting this information on your site - but be aware that the texturized version of Safe 'n Easy is higher NSC and I did not evaluate it) - versus the Nutrena - 22.8% (a reported number, not confirmed with the manufacturer). Lower is better for our horse population.
So, I recommended to our barn that we stay on Equi-Balancer and I'm happy to continue driving to CPI to pick up the Equi-Balancer - it's a pretty drive and I only have to go once a month or so.
I subsequently looked as well at Triple Crown Lite (9.3% NSC - thank you, Triple Crown, for putting NSC numbers on your site) and Low Starch (13.5% NSC). Lite is designed as a vitamin/mineral balancer much like the CPI feed, but the recommended feeding amount is greater - 2 pounds a day - as it provides lower amounts of certain ingredients than the CPI feed does. But it's also too high in iron for my taste and the selenium levels would also be surprising high, even for our area, at the recommended amounts. Low Starch is notably low potassium, which can be good for horses that are HYPP expressers or carriers. It's designed as a complete feed to replace some part of forage that may be of unknown NSC composition - a situation many people at boarding barns have - we are fortunate that we are able to have our hay and grass tested. The manufacturer does say that this feed is designed for horses that can't maintain weight on the amount of forage they're getting, and does say that if you're feeding less than 6 pounds a day you'll need to supplement minerals. Neither feed is really suitable for our requirements, but if you had a HYPP or insulin-resistant horse, Low Starch might be a good option for you.
Whew! I'm tired now . . .