There are a huge number of FPE panels in my area. I have seen far less buss failures on FPE that I have on all other brands including Square D QO. I have never seen any wiring or equipment damages as a result of FPE Stab Lok breakers failing to trip.
99% of the pictures of damaged equipment or wiring I have seen blamed on FPE breakers have nothing to do with the breakers. They were caused by poor workmanship, improper torque, etc.
The questionable breakers are only the 2 pole and were only manufactured during a short time period.
There are several large breaker shops in my area that sell used breakers. They test all breakers prior to sale. According to them they don't see any more failures of FPE than any other manufacture. Of course the breaker may trip fine during the test than not trip in the future but the same can happen for any breaker.
Considering Schnider Electric (parent of Square D) is still manufacturing and selling millions of thes panels they must not feel ther is much of a safty issue. They have no reason to have a huge liability for a product when then have other products that could take its place (QO and HOM) and not loose sales.