I've been playing with the new nozzles for the past two days and just as I had expected it is very difficult to compare them with only one atomizer. It is possible to change the positive post without completely removing the coil but it is quite fiddly. Even so, it is impossible to remove variation in coil position and wicking from the comparison, and the time between vapes is significant.
I do notice changes in flavor and in the sound and feeling of the draw with each reconfiguration. It's more of a difference than I expected but still not enough to conclusively say that one is better than another, including the stock adapter. This experience is deep into the murky territory of subjectivity and possible confirmation bias. The overall tightness doesn't seem to change, but note that I am vaping on the smallest sizes of the adjustment ring. Throat hit seems the same. I had expected that these nozzles, especially the round hole, would reduce the initial gurgle I sometimes get on the KFP when excess liquid has wicked onto the deck, but this is not the case.
Another thing worth noting about my perspective is that I am always trying new liquids. I used the same one (a NET from Truebacco) for my comparisons of course, but I'm not that vaper who's got an ADV that they've vaped 5000ml of and taste in their dreams. This person would have a much easier time comparing these nozzles! I'm not planning on buying another KFP anytime soon so I don't expect to have a definitive favorite nozzle for some time if ever.
My initial impression is that these nozzles do make some kind of difference in the vape quality, but I was already getting a very good vape and I'm still getting a very good vape. I recommend this accessory to the curious KFP loving NET enthusiast flavor chaser with $15 to blow and the patience to rebuild their device several times. Also you will need a 5mm nut driver. To those who are looking for the KFP to be completely transformed, I say try a different atomizer.
I'll update this thread with any further observations as they arise, and I hope you apes will do the same.