shower plumbing costs/advice and shower recommendation?

This could be considered a bit OT for diy, but can anyone advise if this electric shower is any good (currently discounted). It seems plumbers don't prefer them as a make as apparently parts are harder to replace/source, and prefer Mira or Triton. lse&PRODID2999&paintCatId Also, I don't think I'd really take it on DIY (not my skill area) but any idea on the plumbing cost via a IPHE for what appears to be a gravity fed system in a flat ( cladded expansion tank on the flat level in a storage closet) ?
The bathroom has never been plumbed in with a shower and has no electrics. There does not appear to be enough pressure for a manual mixer unit for reasons outlined perhaps, though I like the apparent simplicity offered by a bath/shower thermostatic unit that fits to the bath. Would it be possible to have manual fit that would offer a "basic" and low pressure shower as a compromise and save the cost of plumbing ? Or would the lack of gravity really fail the idea before it even started ? Or might it infact be worth doing the thermostatic mixer and bolster it with a shower pump? Opinions and personal experience greatly appreciated.
Thanks Ant

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