The nostrils flare pretty strongly, so I got treated once last year and again this year. It hurts a lot, but I definitely feel it works. It really controls the flaring.
For the nostril Botox I got this year, one side flared more than the other, so the doctor looked at it and gave one injection on one side and two on the other.
But I do not think nostril Botox lasts very long. In my case, after about 3 months the effect dropped a lot and it went back to how it was.