I moved my loyalty cards from physical wallet to iPhone ages ago, using that Stocard App. It presents the relevant bar-code and/or image of whatever card is required at Point of Sale.
It can work fine, but some stores are half-hearted in their support of loyalty technology. Sparks at Marks and Spencer is a case in point.
Stocard will work in some M&S locations. In others it won't scan at all. A well-trained assistant will key the Sparks number manually, but other times it gets ignored or I get referred to the service counter.
Today I was in a larger store. The iPhone image worked fine in one area, but a few minutes later wouldn't work at all. I surmise that only the hand-held scanners can read the card image.
I'm reassured that I'm still beta testing the future.