Titan are still in business, selling a wide range of heaters from 10kw to 27kw:
Tankless Water Heaters by Titan Tankless
I did ask a heating engineer what he thought of the 12kw tankless heaters and he mentioned a few things to consider. Doesn't mean "don't buy one", just "be aware".
I hope you understand his sense of humor :-)
In my experience, commenting on systems like this is a tankless task. However I can advise that I would not recommend one of these unless you are fully aware of the potential drawbacks.
Firstly this particular unit has a very low power rating which results in you needing to restrict flow rate when the incoming temperature is low otherwise the water will not get to a high enough temperature.
For example:
If you wanted to fill a bath you would want to open the hot tap fully (about 3 GPM) otherwise it would take for ever to fill. At that flow rate the heater can only raise the temp by 27F which is not enough even in summer when the incoming temp is maybe 75F max.
Add to this the probability that more than one fixture will be in operation at one time then you have an even bigger problem. These units only have 1/2" connections whereas your water heater will have at least 3/4" connections so will not allow as great a flow rate anyway.
For example
If you are taking a shower (I understand it happens occasionally) and adjust the flow rate to give a reasonable temperature then someone opens the kitchen tap. More water will now be flowing through the heater which is already running flat out so the water temperature will drop. You will then jump out of the shower to throw some verbal abuse at your wife, slip on the tiled floor because your feet are wet and end up with a broken ankle and bruised coccyx. They don't mention that in the ad.
One final disadvantage of these units occurs when they are dealing with hard water. The small tubes through which the water passes can get furred up causing reduced flow rate and efficiency.
I have specified similar ones in the past but have ended up using units up to 30kW to avoid the above problems which can often be a problem for the electrical supply.