What is the difference between Flagged, Unflagged and Double Trim?
'Flagged' and 'Unflagged' (sometimes called flocked and unflocked) are descriptions refering to the bristles of a brush.
Flagged brushed have had the last 8mm or so of their bristles split into lots of finer parts, making one bristle seem like many very small ones. This makes for a very soft brush, ideal for gentle cleaning and areas where the windows are quite clean. Flagged brushes are often used when cleaning vehicles.
Unflagged (or monofilament) brushes have bristles which are plain all the way to the ends, making them a little more aggresive in their cleaning method. Although not stiff enough to damage windows and frames they are less gentle in use.
Double Trim brushes have unflagged bristles of 2 different lengths, the shorter and denser area of bristles being on the inside and the longer one being around the edges. The longer outer bristles tend to spread on the glass and reach into the corners of the glass. These are popular 'all round' brushes.
Pencil jet or Fan jet?
Pencil jets emit a small circuler jet of water onto the window where fan jets produce a fine mist of water over a larger area.
Fan jets can allow you to do the final rinsing of a window with the brush still in contact with the glass. They also save water but you may find you need to take a little more time on each window in order to get a good rinse. To get the best from fan jets you need to have brushes with plenty of space between the bristles in the jet area, otherwise the water may spread out over the bristles instead of getting onto the glass.
Pencil jets are popular for quicker cleaning and where the brushes have a denser bristle pattern around the jet area.