Call or Email Jesse Wright. His contact info is:
Internet Parts Sales
It took me under an hour to install it.
Go over to Priuschat.com and search for "block heater" and you will find alot of good information on them. And if you need more info I can email a couple pictures I took while I was installing mine.
They do help, as temprature plays such a large part in the stages of hybrid operation in a Prius. If you can start off at a higher temp the ICE will need to run less to warm things up, saving gas.