No experience, as personally I see limited benefit.
However having looked at how it works, if you end up with scale in your kettle now, I would advise purchase of long barge pole. There seems to be no way the same wouldn't happen inside the small confines of the electric boiler that is inside this gadget.
The benefit appears to be the ability to boil just small quantities of water as required, plus instantaneous.
I Ask myself, how often can I not afford to wait two minutes for my trusty and easily descaled kettle to work.
Seems doomed to go the way of most yoghurt makers.