My vet recommends Purina products since they have superior quality control. She has researched equine feed companies and visited their operations, so she is well versed on the subject. They grow their own feed and control it from planting to processing. I have used Purina Feeds for years and am very satisfied with the quality of the feed and with the condition of my horses. My vet does not recommend Nutrena feeds due to the poor quality control by comparison.
So, I do recommend Purina. I have no experience with 747, but if your horse's diet is well balanced, added vitamins are not needed.
RN and 57 years with horses