Hi Ian, the Sebo Duo received a lot of plaudits on the forums about 18 months ago and everyone seemed to rush out and buy one.
Now the general concensus seems to be that maybe its a bit of a lightweight machine, and while it does a reasonable job there are alternatives that do better, namely the Host and Envirodri machines.
You know what carpet cleaners are like; always looking to invest in new pieces of kit that either make our lives easier or give a better quality of clean for the customer.
I paid £200 (inc VAT) for my second hand Host including 20 kilos of granules that I haven't used yet (and probably never will).
I hope this helps.
Musicman