We've had a Zip tap, a BIBO, a Franke (we still have) and a designer product which i cant recall the name of (as i recall it was about 4K when we bought it as part of a kitchen refurb, so not a budget model).
With regards to experience:
The Zip tap we had was not a boil tap (c.£2K). The tap we had would produce water at c.98C according to the control panel, but it only produced in v.small quantities i.e. not enough to fill a cup. We had Zip in to investigate, every time they came in the solution was to turn the temp down iirc to c.85Cwhich made it useless for making a good cup of tea as by the time the water got into the cup it was cooler and the tea brewed, it was not hot, especially if you added milk to it. We got a full refund from tap as the product was being miss-sold.
We have a BIBO counter top item in the office (c.£500) It produces plenty of hot water, chilled too. Its the second one weve had over a period of about 13 years, and it works absolutely fine, produces plenty of hot water,, just works, but it is a counter top model not an over sink model so may not be suitable for all.
At home we now have a France hot tap (c.£1K), which has a pressurized storage vessel, and produces boiling water, i think the storage is c.1,5l so thats about how much boiling water you can get out of it in one go. I have no idea how long it takes to heat from refill, but that suggests its pretty quick as i dont recall it being a problem. Weve had to replace the heating unit, and when we have done so its been replaced FOC, twice! Weve had the tap c. 5 years.
We havent had a Quooker, so no experience, but what i would say is make sure that whatever you get you understand a) what is supposed to do. After our experience with ZIp it appears that many so called boil taps are in fact not, but only hot water. That may suffice to you, but worth bearing in mind.
If you want to make half a dozen cups of tea, then the unit needs to have sufficient capacity to do that without the need to wait for the tank to reheat and not all appear to be able to do that.
This is all JMHO so HTH. Glenn