My tankless has been going strong for about 7 years. The hot water temperature is very stable and never runs out.
For about 9 months out of the year, my gas bill is about 1/3 what it was with a 30 gallon water heater.
If you do install a tankless and have hard water, be sure to pipe in diverter valves to flush. The flush is pretty easy with lime-away, a small sump pump and a 5 gallon bucket.
I installed everything myself and it was about the same level of effort that is required to install a hot water heater. Extra costs are about $100-150 for diverter valves (2X) and an electric pump to flush. I keep the flush kit in the attic with the heater. The controlloer has a standard flush cycle built in.