With the standard Sallen-Key circuit you only need to change two resistors to control the corner frequency.
What does your circuit do that a standard Sallen-Key doesn't?

 

With the standard Sallen-Key circuit you only need to change two resistors to control the corner frequency.
What does your circuit do that a standard Sallen-Key doesn't?

Basic 2nd order Sallen-Key low pass is just 2 poles.
My filter is 2 poles + 2 zeroes filter as what I am trying to achieve is a kind of all-pass filter (but different from common phaser effects).