AForge.NET produces valid results in its FFT computation routines. However, over the years, some users have complained that either they do not produce the same results as MATLAB, that they have inverted signs, or were puzzled that they didn't work with non-square/power-of-two matrices:
http://code.google.com/p/aforge/issues/detail?id=100
http://code.google.com/p/aforge/issues/detail?id=156
http://code.google.com/p/aforge/issues/detail?id=221
As such, it would be nice to provide a version that addresses all those issues (even if the AForge.NET implementation is correct in the first place). The goal is to minimize user impedance while using the libraries.