Well, I have been using this brush for 2 and a half days now.
One thing stands out a lot, they are the most superior brush I have ever used for scrubbing. It just destroys the dirt with no problem, and it hardly holds on to any dirt.
I ordered the pencil jetted brush and got the fans, I don't mind at all as they are brilliant. They sound like the Gardiner black fan jets but act like the red jets on steroids.
At 209 grams it is heavier, I have been mostly using the extreme this year and its double the weight. I wouldn't call it a brick though, it's definitely manageable. The extra effort to manage the weight is more than made up for with raw scrubbing power, this brush is an animal.
I can honestly say, some frames have never looked so clean. I also love the way the crap doesn't stick to the bristle, which makes rinsing on better.
I have a tucker dual trim which weighs in at around 260 grammes and has more bristles which are the same material (Dupont). This has been my go-to heavy duty brush previously on paper it should be more effective than the X-line at moving stubborn muck, but it must be something to do with the configuration of the bristles and the way they splay that make the x-line brush more effective.
The X-line brush won't be any good if you have windows that require accuracy, that's the extremes field. If you are looking for something that gets the muck off quick though then I would recommend the X-line Dupont for sure. Well worth £46.00.