I wonder about this, I heard same claim before. I however owned 2 of them over the last 5 years(moved a country and did not bring first one). Fact that I bought the second one kinda tells the story.

Honest I never had any issue with them.. maybe if you have a huge house? Or really thick carpets. I find it incredibly convenient and it works well enough, convenient means you can use it every day and do not need to get through that barrier of getting something out of the closet. I have the charging station mounted next to the fridge and honestly I will never buy another kind of vacuum.