Doesn't hurt. Slight scratch n slight burn.
I've had it. They will tell you this but the results will set in from about 3 days to 1 week, with optimum results in 2 weeks.
A reputable therapist will generally offer a top up 2 weeks later if necessary.
I use a doctor for mine. I used to use a dentist but he was diluting it and it was barely lasting 6 weeks but for the same price. This doesn't necessarily mean non doctors are wrong though. They know where to put it, generally.
My female doctor who has it done herself (and just about everything else!) at least knows the ins and outs of how it reacts and the troubleshooting aspect (things like brow spocking, comma lines, etc)
I don't care one way or not whether I look younger; I want to look a well rested, good version of the age I am, and I believe Botox helps with this amongst other more natural things.
Give it a go, enjoy. If it isn't what you expected, it might be your practitioner, or just not for you.