From Tomàs's blog at http://lliscament.blogspot.com/
I used V2 Aero XL125S and V2 Aero XL150SC rollerski for my training in Alpe d'Huez. To start descent you need to adjust speed reducers to lower speed that rollerski will not go very fast and use rollerski brake (behind my right leg) to slow down on turns and to stop. When you need to climb the brake and speed reducers do not slow down rollerski at all.
The V2 rollerski with brake and speed reducers can be used on cycling routes everywhere.
The 15 km descent from Alpe D'Huez to Bourg d'Oissan takes about 26min. Climb from Bourg d'Oissan to Alpe d'Huez takes about 80-90min. - dushyn