#2 How strong is the self-centering spring action?
The spring tension is strong enough to require a minimal dead zone - I currently use (0.04, 0.08. 0.16). The sense of there being a centre facet depends heavily on the spring tension and becomes difficult to feel if the base spring is hobbled to reduce base spring tension. The reason I'm aware of this is because I've tried lower spring tensions with an older variation on the same model. I've also noticed how durable the spring tension and internal precision fittings are when compared to other makes - which is why I've settled on a pair of these sticks.
Spring tension is high enough that purely lateral deflection without any weight on the stick will lift the base along one edge if it does not slide the base across the table-top. I use sticky-mats to keep both sticks where I put them and oriented the way I've angled them. I also rest my hands on the lower supports which adds sufficient weight to prevent the edge from lifting during use - so the spring tension doesn't cause the base to slide or lift when I'm using them.
Bottom line: I think the tension could afford to be a little lower - but not by much. It would be a great improvement if things like this were adjustable - as I'm sure we all have quite different preferences.