I recently installed an Engine Guardian gauge/sensor in my van. It came with a traditional coolant temp sensor, and two sensor leads that bolt to the block. I just used one of the bolt-on sensors attached to the coolant inlet, and the setup seems to work great. Gives me a very accurate view of engine temperature, and once I figured out what the average running temp range was, I set alarms to warn me if it goes above that range. It also has a purchase option that comes with relays, for activating fans at set temperatures. Really easy to install. Might cost a bit more than the other options you were looking at though.
http://www.carsensors.com/Engine_Guardian.html