Hi Jeff,
The Jetted Vikan weighs in at about 435g, we have however just done a deal with a major brush manufacturer for a lightweight brush and this will weigh about 185g.
On the subject of what is the best brush, we have used Vikan for 5 years now and have never found spotting to be a problem.
We have tried Gaz's type of brush the Salmon brushes and have found them harder acheive a decent scrub of the window pane, but many swear by them.
The fact is that you will usually get used to whatever you have been using, and a decent WFP'er will usually be able to get a top class finish with most brushes.
Alex