Firstly, no product will prevent a puncture. If a tyre is going to be pierced by an object, it will be.
Puncturesafe simply seals any such piercing,as long as it is not too big.
Nowever, if your tyre suffers a sidewall blow out, nothing at all will prevent the tyre deflating,,,very quickly.
To "guarantee" the product for the life of the tyre is a marketing ploy as if you get an object through the tyre in any place other than the main tread area, it cannot be repaired any more, and it means a new tyre.