My 4Runner was used to develop the FAL kit for the older 5VZ engine. So, most likely I have been running an electric fan longer than anyone here.
On a hot day and you are running your A/C stopped at a light and things are hot, the mechanical fan will lock up and pull some air. When you pull off and try to accelerate and the fan clutch is still locked fully, it will eat a LOT of HOT if you try to spin the engine to redline. Most likely well over 40 HP.
I used to have a Pathfinder with a 3.0L V6. That fan clutch was very aggressive and would always lock the fan at just about every red light and it would sound like a airplane trying to accelerate away from the light with that fan going nuts. Hated it.
I have never experienced that as much on the Toyotas. The fan seems unlock pretty fast and unloads the engine way better than the Pathfinder did.
So, when the fan clutch is not locked up it really is not pulling a ton of power from the engine. When it is, it will...
Now over the years there have been issues with the FAL fan kit on my truck, and yes it is nicer than the kits they ship. The prototype was nicer, better brackets, and better fan controller.
First issue was the fuse assembly melted down disabling the fan causing the engine to overheat. FAL has upgraded that part and that should not be an issue anymore. A few years later the rubber seal dry rotted and fell into the fans and that jammed them up and burned up the motors. I called FAL and told them it was me with the original prototype and they send me new motors, blades, seal and so on. The only part that was not replaced was the original frame. Later the really cool fan controller that never made it into production failed. They replaced that with the fan controller they ship now in kits which is much bulkier and not as nice.
There are good point with the fan conversion. On engine start you do not get that fan noise until the clutch loosens up. On hot days there does seem to be a bit of power that is not dragging the engine down on acceleration leaving a light.
Overall my experience has had me leave the stock fans on all my other vehicles alone. I run stock fans on everything else.
G