I bought this as I use the TomTom navigation software, and so obviously need to have a cradle and a charger.
To be honest, for the price I was expecting something cheap and tacky that might not survive for long, but I have to say it's surprisingly good - the sucker attaches very firmly to the windscreen, the stalk is stiff and stays where you put it, and the cradle rotates and tightens with it's own lock-wheel so you can reposition it easily but it stays where you put it. The iphone simply clips in and is held firmly enough.
The power supply feels sturdy enough and works.
The only potential issue some might have is that the cradle fits the phone without a case - not a problem for me as I use a phone sock, but if you have a case that's difficult to remove you might find it a pain.
UPDATE - It's now over 18 months since I bought this, and it's still going strong. I note some reviewers since have had problems with the charger - mine needs wiggling in the cigarette lighter socket occasionally when you first plug it in but it's still working. I've also had no problems with it sticking. For less than £4 it's been an absolute bargain.