Overall it works very well, no faster than an applicator and squeegee on really dirty windows, but slightly faster for regular fairly clean glass. For anything over 8ft you really need the 12ft extension pole that Vikan does for about £20.
I have found that for dirty windows you need to have a 'two-pad' approach. Fill the bottle with water and GG3 (or similar) and spray on the glass (or on the pad if you cannot reach the glass), work the wet glass with the first pad, I found that it was often easier to use the pad in a vertical position (rather than sideways like a WFP brush). Having done several windows wet, I then remove the wet pad and put on a dry one and go back over the glass 'polishing' them up. On lower level windows the standard microfibre cloths work well polishing up sections by hand.
For windows that are regularly cleaned then a one pad approach works well - use a slightly damp micro-fibre pad and just polish the glass with it until there are no smears etc.
My summation is that it is a useful tool for the inside of communal areas that would usually need a ladder or are over stairs etc.
The grey polishing cloths that come with the kit are the best microfibre window cleaning cloths I've used, great for a quick polish on low level work.