Experience-based advice on using a Shabbat water heater controller?

Question

http://www.sterlingwaterheaters.com/Index.html

According to this website once installed one may use hot water on Shabbat without violating Halacha.

They have Rabinnic endorsements from the following Rabbanim.

Karlsburger Bais Din - R. Chezkel Roth

Vaad Hakashrus Meged Yehudah

Congregtion Nitei Gavriel R. G. Zinner

Rabbi Abraham Blumenkrantz

Rabbi E. Fisher - Head of Gur Kolel, Brooklyn

Was wondering if anyone has any first-hand experience with them and how they performed in terms of:

1. The time length which it has worked for them without any malfunction (if any).
2. Any Halachic concerns encountered while using the product(ie-The consistency in the water staying heated as advertised,is this more of an emergency type product than for common weekly use)
3. Any difficulties encountered while getting the product installed as well as maintaining the product.