I don’t have a convenient local Sainsbury but got the app to use while staying with my sister. I use the similar scheme at Tesco at home and prefer it in many ways. Having a scanner provided with a place to hold it on the trolley is much easier than having to use your phone. I have to take the cover off to access the photo part for scanning. Then I have to hold it in one hand while trying to steer the trolley virtually one handed. My wrist usually aches by the time I’ve finished. There is nowhere to put it down safely. I worry about balancing it on my trolley in case it either slips or gets stolen. You need to have sufficient charge on your phone to use it. Probably still easier than going to the check out. But not ideal