Multivitamins are also known as "expensive pee", because most of what you take ends up being pissed out.
My suggestion is to go to the doctor and find out if you're low on any vitamin, then focus on that. Or if you're lazy like me and don't mind wasting money, then sure. Multi Vs are fine. But the Vitamin industry is basically like the pharmaceutical industry. They will do everything they can to convince you that you need something you don't.
As long as you have a healthy diet and get a good amount of sunlight, then you probably have everything you need.
Also, on a beard level, it provides very little benefit if any. Hair is dead the moment it leaves your pores. Some shampoos and conditioners can help the hair, but vitamins won't do much.