I've waited two months to write this review, just to be sure that the product was as good as I thought.
It is, indeed, and excellent windscreen mount. It has been on my windscreen the whole winter, completely stable while attaching and detaching my iPhone 4 several times on a daily basis. If feels as solid as I could hang myself from it. Also, attaching and detaching the phone to is an easy and comfortable operation that can be done with one hand.
I couldn't be happier, and I fully recommend it.
Edit: one year later, and regardless of how much careless I put or remove the iPhone from it, it's still perfectly attached to the windscreen, rock solid.