If they think these will take off i recon they are wrong. Retro fitting them will always have problems as the wiring cannot be guarenteed. Fair enough in industrial but not domestic. At 211 for 1 unit. I seen a picture today of a cu with main switch and 8 of these and a spare 2 way space. Didn't have cost but the board size is crazy would need to fit a extention to property to accomadate a new CU. Recon 5 years untill they try impose these.