Well just remember, unfortunately, that not everyone wants to mix their own feed, and many high performance horses can handle grains. That's why almost every hunter jumper barn I've been to uses strategy successfully.
I recommend Strategy GX to this user, because if he/she's feeding calf manna, they obviously want to save money and want to see results. Custom mixed feeding is expensive, so I always say do what you can. I personally feed beet pulp and rice bran if I have to feed something else, but I often stick to just the best quality hay I can find. Every horse and every person is completely different, and so I say tailer your advice to the user as well as your own preferences. Just because I hate Purina and hate their how they do business and will never buy Purina products doesn't mean people won't see good results with their horses, because they will.