Originally Posted by DannoXYZ
Yes, you can adjust them with the same amount of precision as threaded headsets.
How would that be? Not actually having had one apart, I'd assume you just push the stem clamp thingie down until it stops and tighten the allen screws, making sure the bars are straight. How precise is that? When I adjust my hubs after repacking, I turn the cone a fraction of a turn at a time to get the clearance exactly right. Same with the adjustable cup of my bottom bracket. It's a micrometer-like adjustment. A threadless headset seems agricultural in comparison.
They also come in both ball-bearing and roller-bearing versions. I like the roller-bearings since they can withstand more load and lasts longer. Notice that on my bike above, I have the roller-bearing Stronglight threaded headset (62gm) and I've left enough extra steerer tube to use with a threadless stem if I wanted to...
Now, roller bearings are something that make sense. They started using them in some motorcycle steering heads 40 years ago.