I finally had a chance to use the K2 Lock Jaw adjustable ski poles and am very pleased. The setting was 3 days at a ski area, but these poles have features that would make them good for sidecountry/backcountry skiing.
The pole easily adjusts to the desired length within a wide range, with very clear markings. I spent most of the time at 5cm (2in) shorter than my usual length (120cm instead of 125cm) and felt they encouraged me to be more forward on my skis for good pole plants. The locking mechanism is very solid at present and seems like it will be durable for the long term. The shortest setting is convenient for transport and storage. The grip was very comfortable. The poles are marked Left and Right, though there isn't much difference between them and I did not notice the L/R until the second day. The straps are good, but perhaps a little short for people who prefer to put their hands in from the bottom and grasp the pole from above the strap. The baskets are for powder rather than racing. The price was more than basic poles ($63) but a drop in the bucket compared to the overall annual cost of skiing.
On a long traverse across a steep slope to access advanced terrain, you could quickly adjust one pole longer than the other to compensate for the slope angle. Also, there is a crude inclinometer feature that lets you estimate the slope angle by putting one pole in the snow vertically and the other horizontally and reading off the slope angle where the poles cross.
I only have one concern: When removing my skis, I push down on the heel release with my pole. I don't know whether that will put too much stress on the locking mechanism and eventually cause it to loosen. Is there a better way to pop the bindings? (I usually do the second one by stepping on it with my boot, but don't like to do the first one using my ski.)