I've tried it as samples (D&H will send some out to you), but I'm afraid I've stuck to Blue Chip, which is about £6 more expensive a bag, but the results are good!
I have a friend who's old mare is on this and she rates it very highly.
I use Baileys lo-cal even though my horse is a TB and not a particularly good doer. It is basically a feed balancer and contains the same ingrediants as blue chip/ top spec but is only £18 a bag.
Since I've been using it Chance has looked fab and for the first time in 8 years his feet are improving
I use ultimate balancer, and find it very good - my horse is lammi prone but under weight and needs to build muscle, so the low sugar/high protein/high vits + mins combination is ideal. Gives him enough energy for competing without blowing his head, and I like the fact that you only use a small amount, as I hate large feeds!