Ease of use when done correctly.
I've had to have a new roller after 2 years which Dyson sent free and i fitted.
I can honestly say having had this hoover for 3 years, I have only ever had 1 complaint the roller went and was replaced free of charge after 2 years.
When used correctly i.e. you don't lug it up the stairs you place it at the bottom and the hose stretches out to reach each stairs its a joy to use.