First of all, thanks for taking the time to post your review. I found it insightful and I'm glad you did it. Please don't let the fact that I have a couple of nits to pick discourage you.
Although I can't see the particulars of the malfunction from here, you should have been able to fix this without resorting to the KNS pins. If your pin is walking out every 5 shots there is clearly something assembled incorrectly. Have you much experience with AR rifles? In the factory design the hammer and trigger pins are both retained by spring wires that rest in grooves on the pin. I am not familiar with your aftermarket trigger but there should be something built in specifically to retain those pins, and it was probably just a matter of moving a spring leg.
This has been the standard of the AR family forever, though looking at my M16A1 and M4 uppers the rod actually contacts the barrel nut rather than the handguard.
Okay, this is something of a pet peeve but I absolutely HATE when people use the abbreviations FTE or FTF, for the simple reason that they aren't uniquely defined. "FTE" can mean Failure to Extract or Failure to Eject (FTF can be Failure to Feed or Failure to Fire). I know some people are likely to claim that there is some convention on this forum or across the internet or whatever that everyone has agreed on a meaning, but I call bullshìt, I have been cruising online firearms groups since the days of usenet rec.guns and I have seen the terms widely interchanged. They are therefore meaningless, I read your post carefully twice and still cannot say what kind of problem you were experiencing. It's a shame to have an otherwise good, informative post like this undermined by lazy terminology that leaves people guessing.
That being said, neither extraction nor ejection failures are usually influenced by magazines so I'm scratching my head how you figure you stopped whatever problem you had by changing mags.