I don't use this myself and have purchased this for my wife. She has a ton of different brushes, bith hair and makeup. She however did not have one of these round brushes and expressed interest in owning one of these. The purchase price was right, being lower than what she had seen in the stores, and once she recieved it said it was also constructed much nicer than most she has seen, rivaling those at a much higher price tag. The round part is about the size of a large orange/ small grapefruit and is a strong plastic. It doesn't collapse like i thought it might but instead is rigid and maintains its shape. The handle is quite short, so if that isn't your thing this would not be for you. However she has no issues with that and tells me it works great for blow drying her hair and has cut the time doing so down dramatically, allowing for more airflow through her hair.
She is happy with this purchase and would buy it again if needed, but the solid construction of this brush means it will be around for a long time.