I've been getting botox every 3 months for around 1 1/2 or 2 years now. For me, it has made a HUGE difference. I went from migraines pretty much 28 days a month, sometimes every day of the month, to now usually having 3 a month, with severity and duration being much less. Lately, I've been having a couple more, maybe 6 in the past month, but NOT bad at all--I can still function pretty well while having them. And docs agree, it's likely just because of unusually high stress levels.
As for side effects, only thing I have ever had is the inability to raise my eyebrows. That hasn't exactly been a problem for me though! The injections are not bad at all. 31 total, all around forehead, scalp, and some down the back of my neck into upper parts of the shoulder. They feel like tiny bee stings, lasts only a few seconds or a minute, whole thing takes less than 5 minutes. Then you just go about your day, no restrictions or anything. Injections may take a couple days to kick in. Just be sure to schedule your next appt (in 3 months) right away so you can be sure to get in when you need to and you don't forget. I do 3 months pretty much to the day, and by the time it's getting closer to have it done again, I start getting minor headaches, usually around a week or so before it's time.
I know they don't work for everyone. But they have been a life saver for me. And really, no side effects, unless you count the eyebrow thing. I don't. Another thing to consider (if you're hesitant) is that the botox wears off after 3 months, so any side effects you have are really pretty temporary. I also get botox to reduce spasming in my bladder and to stop a twitching/spasm thing in my right eyelid. No problems.
Only thing I would recommend doing before getting the injections is to find out if the doc who will do them has experience doing them. Also, don't hesitate to talk to the doc and ask any questions you have, including about possible side effects, etc. As I said, I'm very thankful my doc suggested it and feel that it's really no big deal to have done. But I totally understand being nervous about doing it the first time.
Let us know what happens!