Supermarket fuel goes through the same testing and processing as the fuel in other outlets, although Shell, BP etc will make claims about their fuel being more efficient or better at clearing carbon deposits. Regarding the RON rating, you will not experience any damage to the engine but you might find Shell V-Power (the most highly regarded premium fuel) gives the engine a fraction more power than the 97 RON supermarket premium fuel. It'll be a very slight difference if at all, so we'd try both and see how it drives.