You should just Google search how they make fem seeds. A few different techs and some breeders keep there ways secret.
I prefer them as do a lot of people because you don't have to worry about weeding out the males. Don't really care about doing any breeding so why have to worry with the males?
IMO yes they are worth the extra money.
I've never had ANY female seeds (from the attitude) turn out to be male. And only 1 hermie(Burmese kush)