In the end i went for an undersink Merlin RO unit. We love it - the water tastes great, and its much more economical than alot of other RO units. Its also great for washing up stuff and filling the kettle because you get no limescale buildup. Demineralisation of the water does not bother me because 99.9% of mineral intake is from food, not water. The very slight drop in pH is also of minor concern because i consume plenty of alkalising veg.