My own fan jets are inside the brush, just like the needle type jets.
A line of the bristles in the brush are removed to alow the full width of the fan jets to work.
The spray is contained by the surrounding bristles.
In use you have a spread of water going the complete width of the brush.
It is probably a very personal thing though, most use either one or the other and swear by them.
I would personally like to read a reply from someone who uses both types on a daily basis, and their observations on the differences in use.
Ian