DaveW,
Customisation is taking a standard 6ft section pole and making it into a 5'3" section pole. By using this service you can have a pole of any section length you wish. This makes the pole far more usable on ground floor windows and also easier to reach the clamps, hence quicker to extend.
Spotless2000,
I use the 12ft Extender for ground floor windows as it is very light and has only 4ft sections. The advantage of this pole is if you come across some first floor windows then you can also clean those without changing poles.
Paul Griffin,
An 18ft pole is a good middle size compromise. The aluminium gooseneck only adds about 70gms to the weight of the pole over a plastic one. It has the advantage of making the pole seem to reach a lot further as you can still reach over deep sills without having to step back any further (hence losing effective pole height).
If you wanted to interchange a sill brush you would need Type2 G-Fit, which you could then use a rectangular brush on as well as the sill brush. Or you could buy 2 goosenecks, a type1 and a type2, as they switch as easily as a brush.
Alex