I had ordered a TRS Ski-2 terminal device a while back but only now got around to actually mounting it and putting it to use. It is a great device for the demanding skier.
The TRS Ski-2 terminal device is sold by TRS (link). The details of this skiing pole adapter is best demonstrated on camera by slowly walking around. You cannot get that much out of it on blurry fast action movies when racing downhill; there, the appreciation for the mechanism may easily get lost.
In essence: (1) the pole rapidly folds back when not needed for push (I added some more rubbers (purple - see pictures) to accelerate the pole returning to the back position) (2) it can be extended extremely easily by simply moving the arm forward as that is what cable control does (3) and it definitely is great for planting it into the ground / snow and push action, while (4) greatly improving weight wise symmetry.
Here is how that looks:
Skiing with poles and a passive device - I tried, I do not recommend it, and as poles can get between legs or in the way some other way, this is a real risk in my experience.