I`ve got one of them mounted in my loft. It's been there about 2 years and whilst it does soften the water a bit it only "takes the hard edge off it". My wife still has to use Calgon in the washing machine to protect the element. The kettle still gets furred up and has to be cleaned out about 4 times a year.
We don't notice much difference in the bath or shower so all in all I think it depends where you live. I live near Boston in Lincolnshire and we get our water from the Peterborough reservoir, notoriously hard.