mls is right, it can still cause ulcers, but I beleive when I researched it, the occurance was less than traditional aspirin/bute type products.
I currently use the BL pellets on my rescue donkey because she won't eat the powdered herb form, but we used the herb form on my mom's horse for several years when he had some serious health issues. He did not have any stomach problems with it at all and the straight form is stronger than BL pellets, but much much less expensive than say, InflamaSaver, LaminaSaver or other commercially prepared applications that are available.
It is easy to find on herb websites in the straight form, and there are some good herb books for horses available for dosage. Because my experiences with it have been good, I'm more likely to reach for it before bute for any long term use.