JM You state, "the jury is not stll out". You may not be convinced, but myself and 99% of others I have read see the savings. As an example my summer gas bill is 5-6 therm now with cooking all food on gas and 1-2 loads in a gas dryer each week . Yes I transfered from electric tank, but my electric bill dropped 30$ a month with a 5 yr old Rheem with foam insulation and fiberglass blanket . The electric was set to its lowest setting, apx 105f, if it was set 20-30f higher as many do my verified savings would have been much greater. I save apx 200 a year as I figure it, at that savings I can afford a repair when it occurs.
Without a tank to rot out in 10-15 years, or build sediment and reduce efficiency the tankless life of 20-30 years becomes an even more atractive option . I just pulled out an 18 year old tank at a different location on Chicago water it had apx 12" -14" of rock hard sediment in it, that heater was probably running at 50% efficiency, where that won`t happen on tankless, how much efficiency robbing sediment is in your tank?