We put a 178k BTU >6 gpm direct-vent nat-gas tank-less in a new build for a guy with four daughters and who wanted three full bathrooms to have endless hot water as they got ready for school in the morning. He raised heqq with the builder when temp surges resulted from the appliance's gpm/temp 'steps' vs constant or consistent temp & flow.
My Brother stuck with his nat-gas Paloma

thumbsup

~12 GPM tank-less (& I installed) for as long as it lasted (all of 25 years, btw) but replaced it with a conventional power-vent model. ("I didn't."

) The flush routine offset any perceived energy savings, and to him temp surges were at least as noticeable as with any setup he could recall.
A lot of the push to tank-less WH is from the industry just broadening their market. Commercial use often demands endless hot water, but I'm sure those with experience will admit that energy savings & at home convenience are not as easy to evaluate. (& 'cost' isn't deductible.

) They are nothing to be dismissed, but use may be best appreciated when otherwise-distance to a fixture is greatest and not too much is expected from a mass-conversion. ("three times a charm", but too often "three times a lesson" Glynn's pilot needed re-lit monthly, the only guy who liked his. ~2-3 gpm in 800sq ft bachelor pad.)
Was it here that I caught the idea to just add a small tankless to a remod or addition far from an ok system w/o high hopes? Plumb the remote, tankless or tanked, so that it's fed from hot vs from cold. Short-order hot water until HW from 'main' reaches and the remote then cycles off. I can also augment the 'main' say if/when it's your anniversary and you .. well ..