I used to sell Kirby cleaners. They work very well, but are way too expensive. I have also read quite a few consumer reports over the years on cleaners (I've bought four cleaners over the past 25 years) - I'm an information junkie before I purchase anything.
It seems that in order for a cleaner to work effectively on hard surfaces you need three things, suck, collect, air filter. many decent cleaners meet all three requirements without any problem. After meeting the fundamental criteria it comes down to attachments and how effective they are. Can they get close to the skirting boards, does it come with a brush etc. These attachments are aften the primary difference in whether the cleaner can pick up 90% or 99% of small loose material.
On carpet however, the only real way to get the dust and dirt is to use a power-head. The power-head 'beats' the carpet to release the dirt and dust. Once the particles get to the bottom of the carpet fibres almost no cleaner will get it out with suction alone.
Cleaners without power-heads fall a long way behind in this test - and even more so if pet hair is involved.
On the subject at hand. From all the consumer reports (Choice
in Australia) I have read, on hard surfaces the difference is minimal. On carpet however, the difference between all of the better cleaners generally comes down to whether they have a power head (big step up from non power-head machines), and then how good the power head is.
When I sold Kirby I used to get prospective buyers to vacuum a rug (or whatever other carpert) with their current cleaner as many times as they liked; 10 or 1000, I didn't care. Then I would go over the same area with the Kirby. On almost every occassion I would get considerably more dirt and dust out of the carpet (we had this little window device with a white filter in it to show the dust and dirt). Only once did this fail. That was with this little old lady using an Electrolux with a power-head - no dirt left for the Kirby to get.
Power is the other issue. Don't get all fussed with the 1800 versus 2200 watt model. Pretty much all decent cleaners have enough suction. The other things to look for are whether the hose will kink if it's twisted (cheap ones will), and how long the power lead is (for some odd reason cheap cleaners often have quite short leads - plugging and unplugging in every room = PITA). For non-uprights, can you drag it around the house without it falling over every three seconds. And, finally the HEPA
filter is also a good idea.
Having said all of this, do I think Dyson is better? Well, I've never owned one, but that is because I have never felt justified in paying the extra $ over the cleaners that I have bought in the same cleaning efficiency range.
I disagree that they are the Bose of cleaners. They do review well, but no better than many others. Is the (typically) extra price worth it?
My 2 cents ...