In my conversion of a Dr. Grip Gel to accept regular ballpoint refills I first achieved a very low force in the mechanism, ~2.5 N, but that was impractically small, so I've now modified it by using a set of two springs and it's up to ~4.5 N, which is close to what I think is an ideal compromise.
I guess that a long stroke is also useful to avoid unintentional activation of a pen. But when this is used, why does makers have to compound the problem of fitting the pens in a pocket by designing the clip so the pen sits higher than it could? Perhaps they think it's easier to grab then, which I guess is true. But: The whole of the clip is exposed as well, and that gives a good grip, usually.
The cap on Pelikan fountain pens is shaped to give a good grip, this could easily be done on ballpoint pen retraction mechanisms too. Perhaps not by letting it becoming a mushroom shape as that could interfere with manufacturing, but a couple of ridges can only help.
Twist mechanismsI don't like them. Mainly because they require you to use both hands, partly because there's no tactile information regarding which position the tip is in as opposed to on most click mechanisms.
One guess is that this kind is used mostly by people who don't primarily see the ballpoint as a complement to their fountain pens, to be used when fountain pens are impractical.
Automatic retraction mechanismsThere's lots of different systems around for retracting the writing tip when you put the pen in your pocket. A good idea in principle, but I've seen very few that works well most of the time. They either work well on thin fabric but grips thicker too hard, grip your shirt too much either when putting it in the pocket or taking it out, or both. Too bad, because it's useful when it works.
Separate buttonsOne button to extend the writing tip and another to retract it is something I'd like to see in more pens as it's a good user interface. Too may times I've clicked a pen only to find I'm trying to write with a retracted tip.
OK, a really good tactile feedback from the mechanism works too.