Don't know bout $400 hairdryers, but I have a Dyson DC35, my experience as a consumer is that:
a) It works ok and is more practical (being cordless,handheld) than my previous vacuum ( a mecha yellow eureka)
b) it's quirky, very quirky.
As a designer I am left scratching my head, it is overly engineered in some parts ( the plastic is riot shield grade), the packaging and installation was simple, clean, I like the design, yet it blatantly says f**k the user in others, this last point is evident when emptying the thing, here's a depiction:
So the manual says that you should not fill it over the line( the first one from bottom to top) , which holds very little, yet it allows you to do so, ( an affordability) plus are you really looking at that line ? while vacuuming? , anyways, when you inevitably fail to do so, all those little holes get filled up with gunk and in order to dislodge them, you have to reach in with a twig, a bloody twig, I even have a special twig in the kitchen just for this purpose, I researched online ( maybe I was doing something wrong), and no, other folks have their special twigs, madness.
On the plus side I had a spider in the bathroom spawn hundreds of little spiders, this thing took care of that business in no time, you even get to see them die as they spin to death while you laugh maniacally, so yeah, good product with room for improvement and questionable design choices.