It is a weak NSAID, with the same risk/benefit profile. Probably equivalent to giving 1/10th of a bute tablet, except the potency in herbal preparations is not necessarily consistent from batch to batch.
I used BL Solution, which has devil's claw and yucca, and found it to be similar in efficacy to 1/2 gram of bute.
Devil's claw is an NSAID like bute and it has a very similar, if not exactly the same, side effect profile to any other NSAID. I don't think there's any reason to believe that consistent use of devil's claw will be "saving your horse's insides."
One other consideration to devil's claw is that it is a forbidden substance under USEF rules- it will test.
"I'm not always sarcastic. Sometimes I'm asleep."
- Harry Dresden