Although I haven't used these with skis on my feet, I've been pushing myself up mountains lately and because of my bad knees I need something to disperse the weight off my knees, especially when I have a huge pack on my back. This goes double for the descent. I'm only 20 years old but a walking stick doesn't quite do it anymore.
I kinda bought these on a whim after being broken down and sitting around my camp because of knee issues after a climb. The first time I used these were up Hunt Peak in Northern Idaho. Covering 2000 feet vertical in 2 miles I figured it was a decent test.
My first time using them was crossing large snowfields that covered Icy streams. For this I used them more as a probe, which is where the extendable feature came in handy. I was able to push into quite a few thin coverings before I tested my weight on them. After this I started up the mountain and until the very very steep part I felt blessed to have the TSP poles to help pull me up. Shortening them to compensate for the gradient I found myself using my arms and my legs to push up the mountain with the shock absorption part giving me the slightest relief on my wrists. I did have some chaffing from the straps after the hike though.
I put the poles on my back for the rest of the hike and it deserves mentioning how compact you can get them, I could fit them nearly horizontal on my pack.
As I started the descent I really noticed the benefit of trekking poles. I slowly learned how to catch my weight with each step down the steep gradient by quickly swinging my poles in front of me. Not only did this make my descent much quicker, it made it much easier on my knees/back. I'd say that if you are a serious trekker buy these poles.
Shop for Trail Shock Pro Trekking Poles by Black Diamond