I can sympathise greatly with those who keep going on about brushrolls on a cordless upright, just because you can see it through the acrylic hood.
However, over time those bristles don't keep their shape. The ones on my original Vax Mach Air eventually stopped being tough at the tip. I feel that Vax are trying to copy Dyson again by having blue strips or brushes and in a similar fashion or a nod to Dyson's latest brush roll bars, however even if an upright has the stiffest of bristles, it isn't always going to guarantee an efficient clean, never mind a groomed look, or a look that says "Im destroying your carpet bit by bit by pulling great big tufts out of it."
Of course suction plays a big deal but then so does the shape of the floor head, sole plate, suction air flow and other variables.