9500w at 230v is 5.57 ohms, but who said the resistance of the shower is 5.57 ohms anyway?
9500w at 240v is 6.06 ohms, perhaps that is the resistance of the shower.
As EFLI said, even brand new showers (and most other heat-producing appliances) still have their power quoted at 240V, even now - it makes them sound more powerful and, in any event, I think that most people in the UK probably have a supply closer to 240V than 230V.
However, this one was an exception since, per the OP, it quoted power at both 230v and 240V ("9.5kW - 10.34kW"). If you don't believe it, do the sum:
Pulling the fuse means if a visitor uses the bathroom and pulls the shower cord, either inadvertently or to see what it does, then at least you won't have a live wire hanging around after they forget to pull it again to turn it off.
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