The brush you are using IS a vikan. Unger just put their name on them & vikan make them green for them only, do don't bother getting a vikan brush.
The biggest problem with the Unger/Vikan brush is the jets are way too close to the centre thus reducing the flow to the edges of the brush. Also, even if you lift off to rinse it can be difficult to get water into the corners of the window because of this!
The best advice i can give you is to buy a super-lite brush from gardinerpolesystems. Either flocked or mono' will suite you far better IMO.