Electric fan MAY give you an increase in mileage and performance but it depends on when/where/how you drive...
Mechanical fans that use a fan clutch reduce the speed at which they spin as the temperature of the coolant (air coming off the back of the radiator) drops. On Hayden thermo fan clutches that happens at around 170F. When the temp drops below 170F or so fan clutch allows the fan to spin slower. That makes the fan pull less air across the radiator AND reduces the load on the engine. The key here is "reduce", it doesn't stop spinning. Depending on which fan clutch you get it will still spin 20% to 30% of the shaft speed.
An electric fan, when not needed, is putting 0 load on the charging system which means 0 load on the engine.
When you are heading down the road at 45mph or so (typically) the air coming in the radiator is more than enough and the fan isn't needed. Once the coolant cools enough the electric fan will turn off and a mechanical fan will slow down... That means while your at a speed that doesn't need the fan the electric fan will give you better mileage. How much better mileage depends on the fan/fan clutch combo you are comparing it to.
Around Town is a different story.. Converting mechanical power (engine turning the alternator) to electrical power (alternator to battery) back to mechanical (electric fan) is less efficient than a mechanical fan. That means you are actually using more power to run the electric fan as it is running than the mechanical.
As for responsiveness.. I can say, with my van that is running a somewhat large motor (7.5L, 460 CI), the motor is more responsive with the Mark VIII electric fan than it was with the mechanical fan and Hayden severe duty clutch. Basically, the rpms move more freely. On top of that, you don't hear the mechanical fan noise every time I stepped on the throttle.
Personally, I like to run my electric fan controller on the output of the radiator (near it, at least). When the coolant coming out is in the upper 160F range the fan turns on. This way the fan is running based on the coolant temp which helps keep the coolant temp somewhat stable instead of waiting for the engine temp to rise and end up trying to cool hotter coolant (bigger temp swings).. I'm using a Hayden adjustable (bulb style) fan controller to switch a big relay. It is something I can find pretty easy if it does die.
As to that LMC kit. I doubt that would work. Rick (admin here) is one of the people I've seen try using even the Black Magic fan and even that fan had issues keeping his 4.0 cool in Arizona desert heat and that LMC fan doesn't look very good. The Mark VIII and Taurus (3.8 motor, not the 3.0) fan's are pretty thick and I don't know of anyone who got those fans to fit in the 1st gen explorer yet.
As to, is it worth it.. Well it depends.. A mechanical fan is simpler and while fan clutches ear out over time they last a long time. A electric fan can help but depends on the kind of fan and controller you get you can put quite a load (startup current) on the charging system if you can't use a PWM controller (can't on the higher draw fans).
For reference, the Mark VIII fan I'm using on my Van has a startup current of upwards of 60 amps and continuous draw of 30 amps. Here is a video of when I tested that..
https://www.youtube.com/watch?v=gWJFzAMsIlc . Even with that much draw, even my 1g Ford large case alternator (only 90 amp, and low amp at idle) has no issues keeping things charged, although while stopped at a light the lights dim when the fan turns on.
Hopefully that makes sense...
~Mark