It should last a long time IF you maintain it. It will require more maintenance than a stand-alone WH tank. If you don't make provisions to delime it periodically, the performance will drop and it could stop working in a worst case because the flow through it is so restricted that it overheats internally since not much water is passing through. It's nice to be able to replace it easily, when the time comes, since like anything, parts won't be available forever, too. At some point, it WILL need to be replaced, but it could be awhile. Pick the 'wrong' brand, and parts could become nonexistant next year...then what do you do?