Thank you everyone guys, i received a bad advice from a friend of mine and i would also ask about this extender here! Unlucky i'm in a period where work occupies 90% of my "awake-week" so i got no strenght to read out the internet\the manuals!

Mmm at this point maybe i will go on the Kenko extender but... i can also stay with the 100-400 II clean

Let's see and thank you again