I have a Rennai and love it. Never run out of hot water. I can pop my kids in the shower and rinse them off, take my own shower and the wife afterwards. Pretty cool shit.
Did you have this system installed or was it existing? Mine is a very recent conversion/upgrade from the standard hot water tank, which was 31 years old. The Rennai system, which includes a pressure regulator, circulation pump and a dedicated hot water line (needed for the circulation). It cost me about double what replacing the old hot water tank with a new one would have. So far, it has shown to be worth the extra expense.