Well, as I said, the proof is in the pudding. I'm sure Emma will be able to make up her own mind using the Sebo in her own home. Seems to be doing just fine so far, and leaving nice track marks in the carpet.
The whole idea behind the automatic height adjustment is that it works to the optimum height - the balance between wear to the brushroll, wear to the carpet, performance and ease of use. If it wasn't picking up, the bag would be empty and the carpet would still be dirty, which obviously isn't the case.