What is the appropriate interval for Botox injections?

I have recently become concerned about my facial contours, so I am looking into jawline Botox. Many people around me get Botox regularly, so I became interested as well, but since this is my first time, I have many questions. In particular, I would like to know how often I should get maintenance after receiving the injections. I have heard that the duration of the effects varies because muscle usage differs from person to person, so I am curious about the average frequency. I would also like to know if the effects can wear off too quickly, or if the duration increases with consistent treatment. Since costs seem to vary by clinic, I would appreciate reviews and recommendations from those with experience. I am especially debating whether to use domestic or imported Botox.