Hammer on snap fasteners are commonly used in mass produced garments. They are quick to attach and they look good. But when they break, they are difficult or impossible to repair or replace.
I use sew on snap fasteners in the necklaces and scarves I design, make and sell in my Etsy shop. They seldom break and if they do, it is easy to remove them and sew a new one on. Sew on snaps are ideal for people who are sensitive to metal, because there are no metal parts in contact with skin. The whole snap sits between to pieces of fabric.
It of course takes more time to sew on these snaps, which means higher selling price. But it is durability that counts.
You will find this hand felted red scarf-necklace available for purchase here.