I found it to be poor on the old system because it was a long time
before the boiler would come on, by which time a lot of water had been
used. Then the temperature would overshoot by a long way and the
water too hot during later use.

Was your stat installed too high? My boiler cuts in about 20 seconds after
opening a tap. Besides it has enough capacity to fill two baths, so I'm not
worried about the boiler's additional 28kW cutting in. Also, I have a TMV on
the output, so the exact temperature of the store is irrelevent to me.
Temperature overshoot simply means greater energy storage, rather than a
trip to the burns department with the children.

Christian.