billgates: We put in a Stiebel 15l water heater tank in scullery for instant hot water as distance was going to be a bit from main gas califont unit to scullery.
IMO this is a much better thing to put your money into than controllers. Contnuous hot water is great if the califont is close to where the hot water is consumed. The problem with longer runs is the dead leg of cold water that has to be dumped before you get hot water. I'd also rather go up a size to make sure I had enough capacity rather than put money into cntrollers.