I was running into the same issues @phoenixperry was. I downloaded the precompiled libs (as mentioned int the readme) and tried adding them to the xcode project (both in the header compile paths and directly by adding the fftw3f.a file to the project), it didn't work for me. It would be helpful to have a little more detail on how that should be added to the project, I'd like to compare the KISS and FFTW performance.
I was however able to get the example basic project working by going into the testApp.h and changing the FFTW implementation to the basic KISS implementation:
//fft = ofxFft::create(bufferSize, OF_FFT_WINDOW_HAMMING, OF_FFT_FFTW);
fft = ofxFft::create(bufferSize, OF_FFT_WINDOW_HAMMING, OF_FFT_BASIC);
I also had to remove the #define ALLOW_FFTW so that the library wouldn't try to compile in the FFTW.
I assume that would work for the Easy example as well, but I haven't tried it yet.
Adding in case someone else runs into a similar situation, seems like a solid library.