I am about to embark on a bathroom refurbishment and I want to improve
my shower. I currently have a mixer shower which can, at best, be
described as adequate. The head for the hot water is only a meter.

The alternatives seem to be:
an electric shower - major electrical work, but minor plumbing,
probaly not much better pressure than at present and an
unattractive box on the wall.
an integrated power shower - minor electrical, more complicated
plumbing, not sure of the pressure and again a box on the wall.
a shower pump - not really got room in the airing cupboard for this
a venturi shower - this seems ideal, simple plumbing no electrical
work. So what is the dowmside to this. Anyone have any experience
with them or know which brands are best?

A further point. I am thinking of having my water metered for a trial
period but reading the small print it seems that the water board will
not let you revert to unmetered water if you have, among others, a
power shower. Is a Venturi classed as a power shower ?