Used a Duo but found it was like a Toy, so gone back to 18" Long Handled Carpet Brush with Black Bristles, beauty about this piece of equipment is, low priced, can be used on all types of carpets using same Bristles, also you can apply whatever amount of Pressure the job wants!!
Plus maintainance is inexpensive and cleaning is very simple, letting your client see you using it also shows them that you are putting plenty hard work into cleaning their carpets without using their electricity!!
Another PLUS about owning this piece of equipment is that you can also use it to dress the carpet with after cleaning!!