Dyson's are great but the filters do need cleaning every month or so, even more so if you sucking up a lot of dust.
The amount of Dyson's i use in people houses at work that have basically no suction is unreal out with the filter a few bangs against the wall and its back to full power.

I have had a couple of customers give me broken Dyson's ,there busted as the filters are blocked and the motor cuts out. 10mins cleaning and there as good as new!!