the only thing about a clutch fan that is efficient....is that is is already there......
hence this thing....and why you can get....a genuine motorcraft unit. because the clutch fan is so inefficient at low speed the later units use an electric booster fan for cold ac.....this allowed for clutching and weight dynamic changes that would trash cooling ability but combined offered the most cost effective cooling for max use conditions.
the area of power use under the 20-35 mph curve, and frontal capacity can be an issue for cooling under max load conditions.....the way the oem has to package.... it actually is not...as most of us running 300 hp or more the last 30 years in these platforms proved early on.
the clutch fan sux up alot of power on a stock 4 whizzer or 2.9 or 3.0....... the 4.0 is not really bothered enough and i generally would not take the time to put a electric fan on one....so if your not climbing a hill 2 miles a day wot in 2nd gear barely keeping 25 mph.....your probably good to go with an electric.
the oem fans from later focus/kia or whatever small cars will blow away anything you can get from the parts store in aftermarket in terms of reliability.....lasting 2 or 300k is normal. just depends on how you choose to configure.
configuring the run operation is key. pairing a 80 dollar controller with a pair of 5 dollar junkyard fans is a worthy investment.....you install one...and keep one for the day the other dies....and build in a manual setup and your good.