we have one of these, the 2020c. We are in southern Hants so with reasonably hard natural water.
Being non electric you only consume block salt which is costing us about £160 a year.
We had it installed along with a new Megaflo unvented, pressurised hot water system about 2 years ago, plumbing it so we can bypass it (like if we move house we could take the unit with us). Our house is 12 years old.
It cost about £1000 including installation (under the sink) and a non-softened tap + filter for 'drinking' water beside the sink, and a garden tap spur that's also not softened.
Now, what do I think? I am not entirely sure that I'd spend my last £1000 on it, to be honest. We were hoping that it would help towards keeping DS2's eczema under control but I really don't think it's made much, if any difference.
Yes, you can use much less washing powder, dishwasher salt and 'Finish' (don't need either as no residues!) shampoo etc; no limescale; the hot water system should last much longer, the softened water flowing through the radiators should gradually be de-scaling them.
Personally I find the softness of the water a tiny bit irritating. You sort of feel a bit slimy! For a swift hand rinse after soaping, we gravitate towards using the non-softened tap as it gets that soapy feeling off much quicker. And no one's noticed my lustrous hair. 
. But the shower door looks much nicer...
On balance, I'm happy enough that we did it but we had the £1000 to spare at the time.