For the cordless ones, I've used the V7 (I think), and it's worse than a comparable Bosch.
Again, I'm not saying that Dysons are bad or anything... It's just the hype seems to far outmatch the actual quality when you go to use them, and it's taken them years and years just to get competitive.
This is my experience with Cutco knives. They're better than the absolute bottom of the barrel eversharp stuff you can get for $10, but worse than anything that actually looks like a proper kitchen knife.
I think the main reason they get any business is that most people never sharpen their kitchen knives, which is a lot less expensive than buying a set of Cutcos (I get that there's a social pressure aspect as well, but that wouldn't work nearly as well if it were more clear how garbage Cutco's products are).
The steel is mediocre, but not so different from high end German knives (if you want good steel, Japanese is the way to go).
Now I have a Dyson V-8 cordless and it works fine. It runs long enough to vacuum the whole house and a bit more and is more convenient than anything corded.
They feel like a vacuum marketing company more than anything. People seem to like them because they've only ever used $100 vacuums and it's their first time with something better, so it feels awesome in comparison.