PP here again. I pay $280 for crow's feet and it lasts 3-4 months. My Dr. starts with 20 units and this seems like a perfect amount for me. According to my derm, if you get it done regularly(every 3-4 months) it will eventually last longer and you won't have to go as often b/c the muscle will begin to atrophy. I am about to turn 38 and just started getting it done. It's fantastic and didn't hurt a bit. My Dr. places an ice pack on the skin just before injection which distracts the brain from perceiving any pain. I asked if it is preventative and my Dr. said yes, that this was the original use. Mine looks very natural.