I have the solution: I used a saved game to test the changes. In this game I had already researched the whole advances tree and so I added a new advance on the end (after gaia controller) and a new unit with the new advance as prereq. I researched the new advance and after this I built the unit with the effect as descibed.
Some minutes ago I looked in the sience manager -- the new advance is researchable again??? and therefor the unit not available. So I started a new game, cheated the needed advances and everything works fine. A beginners mistake