Yes, fast breeder reactors have been economically successful up until now, because they are very efficient. Although other methods have come along that have also been useful, fast breeder reactors have been a useful tool in nuclear energy. They were economically successful because they were so efficient and required very little fuel supply. Although other methods are successful and have been developed, that does not mean that fast breeder reactors are not economically successful as well.
No, fast breeder reactors have not been economically successful up until now, because they have struggled to be profitable. They are one way to harvest energy, but there are many other ways that are more cost effective, and that carry less risks. Breeder reactors are a positive scientist development, but they are far from cutting-edge technology.