The first one we purchased lasted until about a year out of warranty, then is started leaking. Luckily that was discovered early and no water damage was done. I disassembled the unit and discovered the following:
Unit has a steel (maybe stainless steel) tank.
Unit is well insulated.
The complaint is the unit transfers water near boiling temperature through a short length of plastic tubing. The tubing finally succumbed to the extreme temperature and failed. Had they used different material here there would have been no failure, but then there would have been no reason to replace the unit... around a year AFTER the warranty ran out.