Depends on your home's hot water needs. If you need lots of hot water for endless laundry, teenager showers, filling garden tubs, then go for it. If none of the above apply, you may never reap the economic benefits of one. Installed costs are very high compared to conventional water heaters. Btu loads are high also, possibly requiring your fuel piping to be increased in size and combustion air needs to be increased greatly also. Unlness you pay $$$$ extra for a direct vent model. They have their place and may fill a niche for folks with high hot water demands, but may not benefit everyone's needs. Go into this with your eyes open and beware of sales hype- I know people who are very, very happy with the decision to go tankless and some folks who absolutely hate them.
The installed costs may never pay off in fuel savings and due to possibly long wait for hot water depending on how your home is plumbed, a lot of Btus get literally wasted for just hand washing or other small hot water needs. On the other hand, we have several in laundry facilities and other high hot water demand situations and these owners have long reaped the benefits.
When a rep came to our office telling all the virtues of these units he addressed the long wait issue in a true, but ironic way. Install a storage tank, he says... OK, now... isn't the one big sales pitch storage tank losses? I am not biased against them, but I would not sell one to someone who does not need nor will not benefit from the good points of owning them. And don't let someone tell you this brand or that brand is the bomb. The various brands have their good points and while some are literally better than others, they all need one thing- periodic maintenance and repair. There are lots of mechanical and other parts needing serviced to these babies compared to low tech, lower efficiency water heaters.