Before revision:  Even though the complexity of the algorithms implemented in SHTns are of order O(N^3) (where N is the maximum harmonic degree of the transform), they perform much better than the available implementations of asymptotically fast algorithms, even for a truncation as high as N=1023.
After revision:  Even though the complexity of the algorithms implemented in SHTns are of order O(N^3) (where N is the maximum harmonic degree of the transform), they perform much better than any third party implementation, including lower complexity algorithms, even for a truncation as high as N=1023.