Yes I have, and I highly recommend this company. With all the advice we all get about how to feed our horses, trying to guess what minerals they need (based on guessing, not true knowledge), it's scary to think about what these poor horses are being fed unnecessarily!
If a person wants to balance their horses' diet, it might be a good idea to find out what's missing first, right? This is the company that can do it, and do it correctly.
Again, I highly recommend them and we use them all the time on the Cushings/IR forum for diet balancing and mineral supplements.