I rented a room in a house (more than 10 years ago now) where the owner bought a Sebo because he didn't want a Dyson and the woman in John Lewis said it was much better. To me it was an over-priced regular vacuum cleaner – nothing special to distinguish it (and justify the price) over any other conventional bag device. His cleaner was never particularly impressed by it either.
When I moved out I bought a Dyson. I still have it for use in the garage (its duties in the house were taken over by another Dyson). Apart from the power switch (which is stuck on, but hardly the end of the world) it all works as well as the day I bought it.
I agree that you see lots of Dysons at the tip, but then they are fairly popular (far more so than Sebo / Miele), and as has been said above they are fairly easy to repair/refurbish so tend to be worth separating out and 'recycling'.