For me this kind of app never worked. It seems they are more useful for first world countries where there are better offers and rewards disponible for its citizens.
Furthermore I see many of these apps consist in cashback feature. What means you need to spend money in order to recover part of your payment (few percents). If the goal is to make money I don't see much sense in doing this, as you are spending more to recover less. Although it can be interesting for someone who is going to resell stuff if he is able to find very good offers, but unfortunatelly it is a very dried market nowadays.