I'm sorry you such a bad experience. However, from my experience, talking with many others, and conversations with many doctors, I can confidently say that Botox is usually tolerated well (of course there are exceptions).
I'm going in for my third recent Botox treatment (I've had 4 or so overall) in a week or two. Generally I haven't had very positive results from the treatments but the worst that I've experienced has been a few bad headaches later in the day of the treatments.
Also, a word on its effectiveness. I don't know if the 25% success rate that you mentioned is accurate, but it's a very good number regardless. With severe, treatment-resistant headaches, a one-in-four chance is very good.
Anyway, again I'm sorry that you had such an ordeal but I just want to make sure we're not unnecessarily scaring anyone away from a common, potentially helpful treatment for headaches.
DX: NDPH (2003-present), CRPS (1998-?) possible Abdominal Migraine (2010-present)
RX: Lamictal, Indomethacin, Propranolol, Provigil, Viibyrd, Oxycontin, Clonazepam, Zyprexa, Melatonin, Magnesium, Boswellia Serrata extract (Boswellic acid)
CPAP for mild sleep apnea
PRN: Ketamine nasal spray, Oxycodone