The unit you linked at HD, an Ariston GL2.5, must be listed with incorrect specifications. It is not tankless. Even if it were tankless, a temp rise of 45°F at 168GPM (gallons per minute!) flow-rate rate is IMPOSSIBLE at 1,500 watts.

Searching elsewhere for "Ariston GL2.5" finds an Ariston sales brochure that describes it as a 2.75 gallon TANK unit, with a 7 GPH (gallons per hour) recovery rate at 90°F rise (incoming water 50°F, set temperature 140°F) which means you could drain and reheat the tank about 2.5 times in an hour. 12.5 amps at @ 120 volts (1,500 watts), which means it should be on a dedicated outlet. It may work for you installed in-line with the HOT water supply at your sink, to catch the "slack" until the hot flow arrives from your main water heater.

The GE shown as an alternative is also a 2.5 gallon tank unit.

The Bosch PowerStar AE12 is a true tankless unit, providing up to 72°F temperature rise, meaning if the incoming water is 50°F the output will be 122°F. It requires a 240v power supply and can pull up to 50 amps, which is more than an electric clothes dryer. Dryers are typically on a 30 amp circuit. Electric ranges are on 50 amp circuits (to handle all the burners and oven running simultaneously). 50 amps @ 240 volts is approx 12,000 watts. The smallest electric tankless Bosch offers provides up to 41°F temp rise (at 0.5 GPM) and runs on 110/120 volts, but pulls 27 amps (3,400 to 3,000 watts) which means it probably must be hard-wired to a special 30-amp circuit.

" want hot water on demand at my kitchen sink without increased bills for electricity, water, or gas."

What you want is physically impossible. The energy to heat the water has to come from some where. You have to decide which is the lesser of two evils for you. Having hot water that takes a while to get there, or spending even more energy on having hot water there when you want it. Retrofitting a tankless of any variety is a huge budget buster unless you can easily DIY. Even then, an electric tankless will probably require new service to your home. Gas tankless is easier retrofitted, but not so cheap if you have to pay someone to do it. Mini tanked units like you show can help with the issue of having hot water right there when you want it, but they do not come at zero energy costs. NOTHING does.

blue - I have no answers but I love your conditions, "... anyone not affiliated with/against the products..."

I will have to quote that if I ever feel the need to start an Aga thread.

I think means not a significant increase and not more than she is already spending for that from the water heater already.

If you're really concerned with the environment look at the efficientcy rating on a given heater. Better rating means more heat made from a given amt. of fuel/energy.

I have an Artison unit in my kitchen. They are TANK units.

I do not use it to 'heat' water, but to solve a problem I have. My hot water heater is diagonally across the house from the kitchen, a d it takes forever (say 45 seconds) to get hot water to the sink. This wastes a lot of water, which is very expensive where I live. So, what I wanted was 'instant' hot water without wasting water. The Artison provides this.

I feed the output of the main hot water heater (in the garage) to the input of the Artison. The Artison is adjusted to about 110 F, whereas the main heater is higher. Thus, the Artison does not 'heat' the water, it just maintains the hot water it is fed from the main heater, without water waste. This works fine.

However, I STRONGLY doubt the use of the Artison to be the only water heater for a kitchen. It simply takes so much energy to heat up water that a normal 117 VAC line cannot provide it. The Artison is really intended as a hot water heater for isolated hand washing sinks in factory and gas station bathrooms and the like.

To see for yourself the power required, check out the link. About 2/3 the way down there is a chart entitled "Temperature Increase Above Water Temperature (°F)". Normal sink flow rates (for kitchens) are generally 1.5 gallons per minute. Anything below 1 gallon per minute will cause you to go mad, so use that as the absolute minimum. Let's say you want 110 F water (HOT dish washing water). Your incoming water is at 55 F. Thus, you need a 55 degree F rise in water temperature. If you look at the chart under the 1.5 gallon per minute column, you cannot get a 55 degree F rise! The most you can get (with these units) is 44 F. You can get it at 1 gallon per minute, but it requires a 240, 65 amp circuit. This is more power than most whole house air conditioners!

Here is a link that might be useful: Water heater rise chart