Don't know how it looks in dyson vacuums, but in every brand I've tried, bagless vacuums are a disaster. They either don't filter that good, require special cleaning or both. One bagless vacuum I've recently used was designed so awfully, I joked that it should come with another vacuum to clean it. From what I've seen in pictures, Dyson's designs are much more easy to clean.
It's funny I had a few friends locally raving about how good dyson vacuum-cleaners were. I thought my existing vacuum was just fine, but I borrowed an upright from a friend for a few weeks and when I did I was hooked.
I started out by vacuuming the floors with my existing machine, and used tried the dyson afterwards. The amount of stuff it sucked up was very surprising.
Sure the dysons are a lot more expensive than the generic machines, but I have to say that I loved mine. It's only because I live abroad now, and I don't have carpets that I've not looked into getting another.