I've fitted, well to be correct, helped a friend fit those ~ he used to sell 'em. Piece o' cake as long as there is the space to work in, trouble was that so many people wanted the bloody things in the most inconvenient spaces imaginable. Some wimmin had it all planned for a cupboard bloody miles away from the water inlet and nowhere near their taps either. Never occurred to them that the fecking water had to go into and out of the bloody contraption so we'd turn up on the appointed day and the lady of the house would announce that her husband (with whom my mate had discussed the matter and quoted to) was (a) not there because he was at work and (b) she had emptied a "more suitable cupboard" in the back bedroom because she didn't want to lose storage space in her kitchen. Always said with a girlish giggle and the words "You boys just don't understand kitchens"
We walked away from several jobs telling the housewife that we would only do the installation when her husband could be there.