I have no first-hand experience with one, but from the photos they look to be the Germans' direct competition for the Elcan OS4 and the 4x Triji ACOGs. They look to be heavy and clunky, not to mention quite bulbous sitting atop an AR in the photos that I have examined. The first-hand reality, of course, may be different. It would seem that you are the only one who can say for sure. Personally, given that the Brits just selected the OS4 as their standard infantry combat optic after taking a look at all of the current offerings, my opinion is that the OS4 is the superior optic at the same (or or close) price. YMM obviously vary.
I was interested in the ZO4 for my G36k clone until I saw the size of it relative to an AR. It would look absolutely ridiculous with an RSA Red Dot perched precariously atop of it. The combined optical assembly would tower over the firearm with crazy height over bore for the Red Dot. No thanks....
Edited to add:
I can't help but giggle at the sight of the monstrously tall optical assembly on the G36 pictured below. Not even a "chin-weld" will suffice to sight through that Red Dot perched atop the Zeiss optic. And talk about the potential for damage to comparatively fragile optics.... Bwaa-ha-haah!!