I've found combi's acceptable for baths and bathroom sinks (flow rate OK,
temperature just about OK if throttled correctly) but in the kitchen you
need somewhat hotter water particularly for "spicing up" a sink of dishes
which has started to cool off. I used to use a kettle but have now put one
of the Screwfix electric tank heaters under the sink, on a second tap.
Perhaps not the greenest solution but very convenient.