You would be forgiven for thinking this was a rubbish item as the brush, when fully assembled, looks and feels flimsy and cheap. However, this isn't meant to brush the entire households' carpets, but for smaller areas of high traffic eg steps 1 and 2 of the stairs, the bit of carpet right in front of the main house door etc. The problem is that it cleans so well, that the rest of the carpet starts to look a bit dirtier than before and you quickly fall into the trap of wanting to clean a bit more, then a bit more until you run out of product.
I would also be good to keep for when you have occasional mishaps or when someone walks in with shoes covered in wet mud or something that should have been picked up by a responsible dog owner!
The diagram on the box would suggest that you just push the brush forward and leave a nice clean carpet behind you - a little misleading. Firstly you need to give the can a good shake, then work in the foam, leave to dry and vacuum up. It is mainly for soiled carpets, if the carpet is stained (especialy if it is an old dried stain), then this may not get it out completely and you may need other Vanish products.
I have a light carpet that is 18 months old and was starting to show a dark area around the front door, this cleaned the carpet up nicely. I recommended this to a relative with a much older carpet and whilst this cleaned the front door area, it then showed-up the rest of the carpet as being slightly soiled too. That being said, it won't be long before its blends in!
In all it is a good product to have, but if your carpet is generally soiled throughout and likely to show up when you have cleaned a small area, you just may be better off renting a carpet cleaner from the local supermarket and doing to whole carpet.