I've looked at the curves of supply, temperature rise, gpm, and pressure reduction and if you are only using it for a single point of service at one time, it isn't a bad choice, but still more expensive than a storage heater. But, if you want to fill a large tub, or use multiple points of service at the same time, forget it. If using gas, for all practical purposes, it needs to be direct vented - and a significant one at that. If electric, you might very well need 300-400A service or more, a rareity in most houses. Yes there are smaller units, and they say 6-7gpm, but if you really dig down into the specs, they'll only be useful under ideal conditions. Most are speced at 50 degree input water. Mine last winter was just above freezing. Another I read didn't recommend it if the supply line was greater than 23', as the temperature loss in piping greater than that meant that the point of use temperature would probably not be sufficient. When using a tank, it is not uncommon to have to mix some cold water in when filling a tub or taking a shower - this improves the volume available vs just from the hot side. WIth a tankless, it is not often once the water is flowing for a moment that you will need much if any from the cold line, thus, your pressure and volume is restricted to what you can get from the tankless unit. Granted, if it is the middle of summer, or you input water temp is 60 degrees or higher, you may need a tempering valve on the output, but that is another hassle - those fail and your output temp can then vary radically through the seasons. I've lived in five different countries, used tankless in a couple, and I'd much rather use a storage tank. All of the volume you want when you need it. Choose a good quality tank, well insulated, and your costs will not be high. Check it out, most good tanks are rated at about 1degree/hour loss. Thus, once hot, the tank doesn't run much. Buy a cheap tank, though, and that standby loss is greater. Hook it to a 93% efficient boiler as an indirectly heated tank, and your efficiency more than makes up for the efficiency of a tankless at a lower cost to buy and maintain. My unprofessional opinion.