I prefer to use a thrmostatic switch that sits in the engine coolant - that one senses temperture in the radiatoir fins.

Sensing at the radiator fin is every bit as accurate. The temperature is just offset

Yes, it reads from the radiator fins - but my temp gauge is reading the engine coolant temp and I adjusted the turn-on of the fan controller based on that. I don't have a clue of the "actual" setting of the fan controller - it doesn't really matter as long as it keeps my coolant in the engine the right temp. What I like (versus the thrermostatic switch) is the adjustability - I would hate to stick in a 180 degree thermostatic switch and have it not keep my engine temp where I want it. Also, no need to tap another hole for the switch. Just my reasoning...I can certainly see doing it your way too!