Is it worth more than a conventional water heater?

Yes. Typically it will pay for itself in energy savings over a conventional water heater. The Marathon will save you energy year after year and after 5 years it won't have to be replaced. The cost of the water heater is usually only half your cost however. Installation is the other cost and you won't have to pay for that and another water heater in 5 years. The other thing people often overlook is the damage to their floor and belongings when their cheaper water heater fails when they least expect it. These failures and leaks often happen when you are not at home.