I think you mean the other way round. E5 has 5% ethanol, E10 10%. E5 is always better than E10.
Nothing wrong with the stuff if it's used fresh, but as it ages it absorbs water and then the ethanol (alcohol) oxidises. Oxidised alcohol is..... vinegar (also known as acetic acid), which corrodes loads of stuff.
But in any 2-stroke carbureted engine, only use E5, because as the alcohol vapourises near the jets, moisture condenses out in the throat. And those droplets make cold starting really difficult.