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I put one of those inexpensive sensors on my Jab 3300, interfaced with my RDAC/MGL XTreme EMS. It worked great, but on hot days after being flown and then parked for a while, it would heat-soak and act erratically until the airflow on the subsequent flight cooled it off, but that mean't no stable tach output during the take-off when you need it the worst!
I finally bought a Honeywell GT-1 sensor which is rated for 150 degrees C, and it worked perfectly even if heat-soaked. However, my sensor is located on the rear of the engine and since the Jab has ram-air ducts to the cylinders, it has less cooling flow in that area. If your sensor is on the front of the engine or has a conventional cooling plenum, this may not be an issue for you.
I believe that WW / SPA figured out a way to read pulses off of the alternator output and cipher that into RPM. Maybe less complexity.
That would be for direct drive alternator only , though.
U are correct
I have the front alternator