Which boiling water taps would you suggest that are best balance in terms of functionality and price? Are branded ones better than cheaper alternatives?

I have had a Quooker since 2010 and I love having it. One of the early ones, therefore, without all the bells and whistles. It is a boiling water tap only. The big difference with the Quooker is how the hot water is maintained under pressure at over 100 degrees which means what comes out of the tap is actually boiling, or very close to. The energy-saving hype is to be taken with a grain of salt. I did a test using a power meter where I measured the Quooker over a week and then turned the Qooker off and measured a kettle over a week. I tried to be consistent with the usage pattern and didn't wastefully over-fill the kettle. There was negligable difference in power consumption over a week. YMMV. I love having the Quooker. I missed it greatly when it was disabled for the above experiment. I use it to fill pans as well as make hot drinks. You also need to service it. The tank will fill with scale, a shockingly large amount of scale. I tear mine down completely every couple of years and give it a good clean out. The other thing to bear in mind is that the product evolves and getting spares down the line may become difficult, I have difficulty getting spares for mine but, like I said, I have had it for a decade or more. I think their new sales model for some of the parts (the scale-control device) is a rental / subscription. I don't have that but get compatible scale filters off Amazon. I had a relative that got a cheaper device (by "insinkerator" I think) that lasted less than 2 years before being ripped out. The water it put out when it worked was not boiling. The Quooker is very much a "lifestyle" appliance. It is very expensive and the spares are also very expensive. If you live in a hard-water area you need the additional water filter. If you want the convenience that it brings and consider the price to be value then all I can say is that I love having mine.