Good idea, but too shaky

I bought today the holders in the media market for my Oktavia. There is it in combination pack with a suction cup (which makes a better impression). But I just wanted the ventilation grille variant. Installation is quick and as well as the dismantling (thankfully). The position and the adjustability are fine, but since the two grip hooks hold only a thin hinged blade and twist out loosely on the ventilation grille frame is, I was particularly with the Navi it ​​too shaky. I was afraid that the whole conglomerate with a violent braking toward the windshield adopted - probably in violation of the slat or the gripper. Too bad it will bring back to the MM ...