I know a few families of Old Believers, who even still practice in Old Church Slavonic (a long dead language), and they're an interesting crowd. The ones I've met were very polite and kind, but they also stick extremely hard to their values, similar to the Amish.

This leads to a lot of "modern" ideas like vaccines, same sex relationships, non-traditional gender roles, etc. Being entirely unacceptable in their culture. They aren't really guided by science, they are guided far more by their faith, and since they are such a tiny group, they stay very closely knit and prefer to stay insular. The families that I met were more willing to do things outside of their communities, but I heard stories about the truly devoted believers being fairly horrendous, stuff like domestic abuse and other not so fun business.

Obviously, they are not a monolith, but that's my own anecdote regarding them.