I have heard about Kerberos SDR and saw the direction finding video.  It's hard to tell how accurate it is.  It's using TOA measurement instead of Doppler.  That isn't necessarily better or worse.  TOA is susceptible to reflections like Doppler.  Kerberos is based on the RTL-SDR which uses an 8-bit ADC.  The Teensy used has at least 12 bits of resolution so I may have an edge with more accurate measurements.  By using the 2nd harmonic which is a measure of reflections I hope to filter out bad readingings.  

I look forward to a fly off between my DDF and Kerberos in the future.