I had a very knowledgeable and trusted mini / pony trainer recommend I give bute to my mini for leg issues she had. We discussed the pros and cons, and she explained the dosing issue. We worked out a correct dose, and it did work beautifully. I agree bute is better for muscle / bone issues. As a side note, she also recomended giving a single prevacid, approximately 2 hours after the bute dosage, to guard against ulcer issues.
My vets have given bute to my minis on several occassions, but usually IV and they are very familiar with minis, their weights, and dosages, and we've not had any problems.
By the way, I give the bute powder, it is easiest to come up with the correct dosage, rather than splitting pills, etc.