It does what it says... But then your shop is unusable with a mobile, because it doesn't just disable long-press and save on images, it also prevents you from clicking on the images... which means collections etc won't open (at least on Android).
I would have messaged the developer to ask for a fix, but when I tried to uninstall it I was presented with a list of instructions, showing you have to mess about removing code manually, which annoyed me. The app says "No coding needed to install"... True, but not that straightforward to uninstall!