shower cubicle walls

My builder, 6 years ago, lined out my shower room with standard plasterboard, which as we all know has the water-resistant properties of a Rich Tea biscuit. Despite his assurances that tiles wouldn't let water through, the plasterboard has inevitably turned to fusty mush. I see Wickes do a cement-based board for this sort of environment, called Aquapanel. Has anyone used it? Any tips, experience or suggestions of alternatives would be appreciated.
Once the underlying walls are restored, I am considering finishing them with Formica waterproof panels instead of tiles. Is this as easy to install as the literature claims? (e.g. what happens if internal corners are slightly out of plumb?)

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