I had the Mule for about 5 years, still had a lot of false positives from passing school buses and transport trucks. Missed about 10-20% of vehicles coming into my driveway depending on weather and how fast the vehicle was moving. Unit stopped working altogether now.
I switched to a eMacros 1/2 mile range solar motion system a year ago and find it catches about 95% of visitors. I have less false positives than the Mule system but it will occasionally go off from a bird or bigger critter with the sensitivity turned to max. I have a second sensor at a farm entrance set to normal sensitivity and don't see any false positives.