the tosefta says that wearing a red string around the wrist is darkei emori and is therefore assur m’d’oraisa. there are probably other opinions, but apparently, rabbi yaakov hillel holds like that. (he’s a mekubal, and he probably knows what he’s talking about.)
As for the “hamsa,” its origins are very suspicious (there is much archaeological evidence that it comes from avodah zara, and the sifrei kabbalah make no mention of the “hamsa”), and according to Rabbi Zev Leff, people shouldn’t use/believe in it, unless they have a strong mesorah for it.
(many sepharadim have a mesorah for it. most askenazim don’t.)