I wouldn't use them for windows if I was you? the pressure could damage window seals, not only that, the lance has a tendancy to jerk when you switch it on and off, do this to close to the windows and the tip of the lance can smash the windows.
It would also drink your pure water in no time at all.
Apart from the above there excellent for doing facias and guttering from the ground, so long as you don't get to close you can also do the finials on the top of conservatory roofs, again don't do the glass or plastic sheet on the roof, again damage to the seals can accure.