Neil,the way it works is you adjust your adjustable gooseneck to set the up or down angle depending how far or near you are working,then when you put the brush on the glass it moves freely left and right,it`s not that loose that it just flops it does has a bit of stiffness to keep it straight but you can also lock it so it can be used in a straight fixed position,
heres a picture of one and of a brush with more bristles than before,Gaz