My Mum's existing Mira Sport shower is playing up and it's probably not worthwhile trying to get it repaired or fixed. I'm not sure of the exact rating of the old shower but it's not especially powerful but fine for my mum. What's the practical difference between the 7.5kw and the 9kw versions? I assume that as the heater is more powerful, it can heat the water up in less time as it travels through therefore allowing a higher flow rate.
Cheers, Rob.