I really feel like it depends on the specific horse as to whether bute is "safer" or more dangerous.
I know that Lacey, who has uvietis and so gets bute during an attack, she gets weird and tummy-uncomfortable on just 1/4g of bute if she gets it daily for about 2 weeks. She has to get 2g of bute/day during an attack but the vet advised a daily low-dose bute regimen to keep her pain levels low during the summer. 1/4g was just enough to ease pain so I tried that. And it went sour fast.
For what it's worth, she also gets really "loopy" on bute. She starts taking risks she would never consider when she doesn't have bute in her system and basically goes a bit bananas. She's usually very sensible but bute seems to take away some of her inhibitions. I guess she's just extra sensitive to it. The vet's seen her on it before and couldn't believe what it does to her. After an episode, after I take her off the 2g of bute/day, she literally behaves like someone withdrawing from a drug. All mopey and depressed for a couple of days. It's ridiculous.
Anyway, I got her on Devil's Claw and Yucca for summer pain-relief. It's similarly pain-relieving but slightly safer over the long haul and she doesn't have any adverse reaction to it. She still gets 2g of bute/day for 3 days during an episode but I try to get her off that and back on to the DC+Y as fast as possible to avoid issues.
Fabio - 13 year old Arabian/Lipizzan gelding
Rest peacefully, Lacey.