i think once you are dealing with very elderly horses, then you need ottake their comfort into consideration - the likelihood is, at 27 years old, that he will go peacefully of old age before any liver problems show up. at that age then bute, devils claw - whatever keeps them comfortable.
but i have heard of plenty of people who use devils claw on younger horses, nd use it to keep them sound enough to work hard, without even considering what they are doing. they wouldn't dream of working theihorse on long-term bute, they'd consider it masking the pain and so on - but they are perfectly happy to give DC, not thinking that it is doing exactly the same thing and in a potentially more dangerous way.
long-term use of anything that is strong enough o have an effect, will potentially have side effects. for me, (cost issues aside, lets pretend bute and DC are the same price) i'd rather it was a clinically tested and well-known drug than something provided by a feed company where i have no idea of possible side effects, of comparable strength, of how it was produced, etc etc.