We had a choice of one of them in our new kitchen but I didn't trust myself with one
I mix my left and right up at best of times and I'm always getting the hot and cold taps mixed up as it is so the thought of nuclear temp water coming out of the sink taps was a non- starter .
We've also got our young grand daughter to consider as well ...
It's set about 1m away form the main sink and tap (right underneath cupboard with cups, tea coffe etc) with a small 15 x 30 sink. Works a treat having 2 sinks and taps as our kitchen is not big enough for two full size sinks set away from each other.
The heating tank underneath the worktop takes up half of the cupboard space below and, I guess if it is to be positioned under your main sink it could get in the way a bit, what with waste disposal and the usual additional waste pipes that tend to be place near the raising main / mail waste outlets I.e. dish washer, washing machine (unless you have utility room of course).
We've got a Zip Hydrotap G4. It has the option to set an on/off/sleep schedule to save power. Wasn't bothered about getting one but we had a new kitchen fitted so decided to put one in. Now we wouldn't be without one.