I have a dart but it is being reaired at the moment and i have a bs 36 on loan, What a pile of poo it is the suction is rubbish compared to the dart and far more clumsy. The only good thing that i have found with it is the large bags!
To be honest i don't think for sheer power of suction and brush you can't beat the Dyson, but the fact that they don't last due to the type of plastic they are made of causing bits to break off and that everybody owns one makes it pohibitive to use in a professional situation. If they made a more robust comercial version that would be good!
Cheers Goron