So in PA the state police use the "Ford Police Interceptor Utility (Explorer)", and the "Ford Police Interceptor Sedan (Taurus)", and my opinion is different. I only buy unmarked units for our family, and I only select models that are low idle hours and low run hours. Higher mileage is of no concern as that means more highway. Door panel, drivers floor, and drivers seat tell the truth on how it was used.
When buying a true unmarked, not used for patrol version of one of these, they can be VERY reliable. There are 3 major areas of failure, the water pump, the PTU, and the rear differential axle seals / wheel bearings. Aside from that there is not much that goes wrong with these. The 3.7L V6 NA Cyclone engine is very reliable, and they do not burn oil or suffer from any cam phaser issues like the eco boom engines do. The 6 spd tranny is near bullet proof. Also if you change the ptu fluid every 5 ~ 15K miles those are reliable too.
In the north where there is salt, these suffer the same rear caliper / rotor issues as other rust belt cars.
I do not need the big space of the explorer, so I choose the Taurus, and I have 202K on it. It has been great.