How long does jaw Botox last?

Perhaps because I have a habit of clenching my teeth while sleeping, at some point my masseter muscles started to bulge, making my jawline look wider. It bothers me every time I look in the mirror, so I am thinking of taking this opportunity to get Botox.

Since it is an injection procedure, I am actually a bit nervous and worried. For those of you who have had square jaw Botox, what is your average satisfaction level? Also, I am curious how long the effects last after just one injection!

I've heard it usually lasts about 3 to 6 months, but does the duration vary significantly depending on the individual? I would also appreciate advice from those with experience on whether regular injections are necessary to maintain it!