You could tell Miele that and see what they'd do in the future. But there's really no need to open up the bag compartment to check the bag unless the bag gauge is fully or almost red. It's just like with gas gauges on cars, I only fill up when it's just about or almost empty.
In all of honesty, I'd go for the D4 over the D1. When the Windtunnel breaks not if, your friend would already have the D4 she'd continue cleaning carpets with. Otherwise it'd be just another waste of money and a trip to go buy a new vacuum for carpets only. Not to mention all the closet space she'd end up saving by having the Windtunnel gone.
