What is this sensor? Is it needed.
 

My sources tell me that it looks like a Fan Switch Sensor when comparing what it looks like in person and on Mazdatrix's website. I am running a black magic electric fan so it seems it wouldn't be needed. Any info would be greatly appreciated...

Also: The sensor plugs into a green wire with black clip as shown in the fourth photo if that helps

More pictures

Yes, that's the auxiliary fan sensor...you could use that location to place the trigger for the Black Magic fan.

How would that location work for an aftermarket temp gauge?

Been covered a lot, not the best spot as you won't get an accurate reading until the thermostat opens. Drill/tap water pump housing. Or use factor gauge location.

As stated you can use the location for a temp switch for your new fan.
Even though the location only reads when the thermo is open I still like to use it for my aftermarket temp gauge.
If you think about it you really don't need to know if the engine is cold*(that would be obvious at start up)..only when the engine is Warm..or hot.

my car made the buzzing noise without it