It was more fuel efficient only over a very narrow band of the entire flight envelope. Also, it suffered from snap-stalls and very poor stall recovery due to its delta wing.
This is, primarily, why you only see delta wings used in super-sonic aircraft where these limitations are more than made-up for its ability to go trans-sonic with (relative) thrust efficiency.
This is, primarily, why you only see delta wings used in super-sonic aircraft where these limitations are more than made-up for its ability to go trans-sonic with (relative) thrust efficiency.