I have used botox regularly between my eyebrows and sometimes in my upper forehead and tried the Dysport because of a great $50 rebate offer. Had 50 units at $2.50/unit (63 after rebate and special members 10% discount)(about the equivalant of 20 units of Botox I think) and I noticed that it only took about a day to go into effect whereas the Botox takes about 3 days to start working.
It may last slightly less as well. It's hard for me to say because I typically just do a little bit every month or so. I would use it again.