They are probably concerned about the magnet setup. The one that comes with the 554-125 is heavy and you should really have at lease 2 magnets. Just hard to set up.

I always use the FAST 301436 (2 magnet) or one of the ones from Motorsprts Innovations.
http://www.motorsportsinnovations.com/Holley/holley-efi-sensors.html

Or if you really want resolution go 18 pulses per rev from:
https://www.motionraceworks.com/uploads/5/3/8/0/53809729/motion-raceworks-dsss-instructions.pdf