Don't expect massive flow or temperature especially in the winter months. In some circumstances such as when very hot water is needed to fill a bowl quickly such as washing up then something like an Ariston 10 litre undersink heater 2 or 3 kw would be a better option, Expect to pay £100- £200 with additional kit if required.
It's basically a hand wash unit
Plenty of kettles are 3kw. 3.3KW is a bit odd choice, because if it was 3.1kw, it would be dead on 13A. It's also convienent if your boiler is a good way away and you want quick hot water rather than waiting for it to heat up (if a combi), then get to you through the pipes.
Kettle basically. Some kettles are 1.8kW, 2, 2.2 kW. Exist powerhouses too...
Can connect it to where your cooker connection is if you use gas and its spare