
You should watch the demonstration video at Zagg website to see for yourself how tough the skin is eventhough it is only .2 mms thick. The company provides lifetime guarantee since they are sure of the quality and durability of the skin. If somehow you can do a scratch on it, they will replace it for free. Additionally it will not leave any sticky residue if you ever need to remove.
According to my personal opinion, the most effective solution is to buy a high quality Nokia 5800 case to protect against accidental drops and buy InvisibleShield against scratches.