I bought the smaller one because it has a machined scraper on the opposite side. Bl oody thing does not work as the plastic adapter they have on it to fit normal poles prevents the scraper edge from touching the glass. Non too happy me. 
Sorry you are having problems with this facility. As stated on the website the the Super-Lite
® Xtreme brushes are designed to work with the new Super-Lite
® carbon gooseneck system. When used with the current plastic socket they will not function to their full potential as you have experienced. There is a new plastic socket in production at the moment specifically for these brushes which will allow it to function exactly the same with a plastic socket as it does with the carbon system. These will be available to all customers who have purchased the Xtreme at a very minimal cost.
As above. Thinking of getting one of these, does anybody have one and what do they think of it?
Our resident window cleaners currently only use the new standard Xtreme brushes as they find them very light with a splay pattern that suits their work methods. They do not use the wide Xtreme as they do not need the extra width. Apart from being wider than the Xtreme they are also slightly stiffer which provides good scrubbing, but does need a little more pressure. Our personal recommendation if you do not need the extra width is to try the Standard Xtreme first.