I've never seen that before.
I have a HotShot I use for up to 16 oz. but you have to add water to the unit manually each time you use it. We use it for instant coffee, tee hot chocolate, etc.
What I found interesting, when reviewing the specs and users manual on that unit, is the fact that it's only something like 750 Watts. My 16 oz unit is 1450 watts and cost $20.
I know different application and uses but I would question the recovery rate. I see it hold 2/3 gallon, so you have some reserve but as you use it cold water comes in cooling what's already there so I assume the flow rate has to be pretty slow if you plan on using more than a small amount at a time.
I know there are a lot of small point-of-use units for under sink mounting but I suspect they are set up with a much lower max. temperature. Common for bathrooms sinks.