In general, fuel additives are good for your engine, mainly detergents, that help keep your engine free of carbon, and ash, by improving the burn. Big brands, like Shell, Esso, and BP, spend lots of pennies on developing their additives, and this is generally reflected in the price, as they are an addition to the base fuel. Fuel without additives still meets the E5 an E10 spec.
The good thing about E5, is that it contains little or no alcohol, (the 5 in E5 indicates no more than 5% alcohol), whereas E10 contains 10% alcohol. E5 is also higher octane, 98/99,compared with 95 octane for E10.
Alcohol is lower in energy than pure petrol, and older engines were not designed to run on fuel with alcohol. E5 is more expensive than E10, but you'll probably benefit a little in mpg, and general running. Your A2 will love you for it.
Mac.