Alot of these power brush type wands like Extracta one, rotovac etc do a good job, But i think i they will actualy add time to a job unless its commercial. The reason being as to do the nooks and grannys, the edging, and corners, and under foruniture you will still need to change to a wand.
So if your doing large open areas often then invest in them.
There are other ways of speeding time up like, filling the buck up while setting up machines, better pre-spray for the job in hand, always ask the customer to empty the room (not always possible) etc etc