After many evenings research I eventually (formerly Exogear) landed in the normal U-Grip from OSO. However, there were "complaints" that the smartphone rather shaky sitting there. And then I came across it at some point, that the "pliers" in U-Grip Ex are wider than the normal U-Grip. So it should be the U-Grip EX - although I would never need this extension.
Now the U-Grip Ex depends for 2 months in the car and it's just outstanding. The mechanics and the two rubbers at the ends of each hold smartphones width completely determined (in landscape mode, of course - I've never tasted portrait) and secure. With cobblestone wobbles nothing. And also nice: Without the extension part of the suction cup disappears behind the smartphone and has more visibility through the windshield.
After some practice I can easily use my Nexus 4 with one hand and remove.
The high price was worth it and I would buy this mount again.