Try one. First vacuum the carpet with your current vacuum, etc. Then proceed to run the Dyson over the carpet and watch it fill up with all sorts of disgusting detritus that the other vacuum missed.

Actually Dyson usually rates far higher in consumer tests than bagged vacuums, and it usually rates slightly higher than most bag-less vacuums.

Vacuum ratings are generally low to begin with, yet still get purchased. All portable vacuum cleaners fall flat on their face in terms of convenience compared with central vac, however not many people are stupid enough to pay thousands of dollars for a slight improvement in convenience.