I get from that RBR post that the issue there is that it was an INTEGRATED headset. Yes, I would avoid those (though I have never even come accross an integration option in any bike I have looked at).

I have owned something like 20 bikes with threadless headsets. None had any sort of proprietary headset. Can you give an example of a frame with a proprietary threadless headset? I am sure they exist, but I think they are very uncommon. Maybe C-dale with some of there oddball forks, or bikes with shocks inside the head tube?

Yes, you can overtighten a threadless headset, but you can also overtighten a threaded one. Not sure how one is more or less likely to be overtightened. I find the preload easier to fine tune on threadless, but that is just me.

You don’t need to remove a threadless headset to pull the stem. Though keeping the fork from falling out does take some planning unless you keep the bike on the ground.

I guess if adjusting the height is something you do a lot, threaded would make that easier. I know this is what GP sells the idea on. Might be very useful if bike is used by different riders.

In terms of performance, For casual use I don’t see much difference, but in applications where I am torquing on the bars hard, I find threadless to be stiffer, and threaded more likely to creak (assuming the threadless headset uses an expansion ring).

To each his own, I guess.