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.

http://www.diy.com/diy/jsp/bq/product/product.jsp?CATID=236&entryFlag=false&PRODID=162999&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