I was initiated into the Kriya Yoga of the Self Realization Fellowship in 1979. Later on, in 1983, I was intiaited into Surat Shabd Yoga, through Sant Ajaib Singh. The similarities far outweigh the differences between the two systems. Likewise, many internal meditaion tehcniques the Sufis employ are quite similar. Not too surprising is it? Obviously, they have a common root source dating to the Vedantic era.