The result is okay. To ensure good adhesion, it is necessary that the dashboard is clean. Well, that's obvious. But we also need the support has been cleaned fairly recently; if not, the initial adhesion (excluding vacuum) is not good, and the carrier falls rapidly.
Then, over time, it does not hold. In summer, with higher temperatures, the carrier does not support a few hours of parking. We must reattach before taking the road, and during the journey, with a controlled temperature in the cabin, it's going well.
Finally, the expected support rigidity is relative: the dashboard is not super hard, and moving slightly. But quite clearly amplifies the support these movements. On a good road, no problem. On a rough coating, support vibrates a lot. Well, it's a little uncomfortable, but that does not stop to correctly read the trajectory proposed by the phone.
In short, the medium is the essential, namely to hold the smartphone (a Nexus 4 in my case). But it moves a little, and it does not take long. My needs are covered! Not sure that the same is true for other more demanding customers ...