Electric fans reduce belt load much of the time, but increase electrical load when in use, often requiring a larger-capacity alternator.

Electric fans can be smaller and lighter than mechanical fans while still providing full cooling at any engine speed, whereas a mechanical fan has to be over-sized for high RPM operation in order to cool usefully at low speeds.

Electric fans are a little more complex, relying on a sending unit, wiring and the electric motor, and so more prone to failure. Clutch-type mechanical fans also add some complexity and an additional failure point.

Mmm. I wonder how much more efficient the e-fans are, in real-world situations.

To run an e-fan, you must burn fuel to make mechanical power which turns the alternator to make electricity, and possibly store it in the battery. That electricity is converted back into mechanical power to move air and cool the radiator. The intermediate electrical step has to be a major loss of efficiency, compared to converting fuel directly into fan power.

I presume that the electric fan looks more efficient in EPA fuel economy ratings, since the e-fan will be off under cruising conditions, and any fan clutch will have a little drag which at cruise will be a parasitic load.

Certainly an electric fan will be quieter, because it will be off on the highway. Fan noise can be significant.

I suspect the main advantage will come under extreme heat stress, like pulling a heavy load up a grade in 100 degree heat and high humidity, with the AC on. At that point, you can likely use extra cooling from a fan running at full blast plus the normal air flow. I also presume that it helps deal with heat soak at shutdown - we've all heard parked car's electric fans continue to run after shutdown. Just like with EFI, servo control provides a lot more flexibility than mechanical control would.