I have many hours of thermaling with other gliders at the same altitude and my PF never failed detecting them. Early on it will occasionally fail to detect mode C traffic further away at any altitude but this had been fixed. After flying with both my Zaon and PF for additional 30 hours or so there was no occasion where my Zaon detected traffic which my PF didn't except that the "afterglow" of the Zaon seem the be a little longer (traffic going out of range continue showing up on my Zaon for another 10 seconds or so).
BTW, I am not affiliated with Flarm or Butterfly but I did some beta testing for them.

Ramy