Please don't mind me for not agreeing with you. You may have coolant exiting the engine at around 210, when the thermostat should be fully opened (I think the stock thermostat is fully opened at 210), but the radiator temp may be 120 degrees, perfectly valid scenario on a cold winter day. By your rationale, the fans will start cooling a radiator that has 120 degrees. Some probes are recommended to be installed where the water exits the radiator or enters the engine, with some of them to be installed inside the inlet engine hose. Of course, I am talking about adjustable thermostatic controlled probes, where you can set a lower or higher temperature to turn on the electric fan(s). There are probes (non thermostatic usually) that you mount on the inlet hose to the cabin radiator/warmer. But I agree with one thing, thermostat housing is one of the best locations to measure the engine coolant temperature.
The advantage of the controller op and I use is that it can be adjusted to start at lower or higher temperature, so the position of the probe on the radiator matters only from the point of view of not being in direct fan airflow, this causing it to cool faster than it should. Again, the only reason I went with efans was that with stock cooling, I was going over 210 very frequently in the summer, sometimes even on highway speeds, since the stock efan kicks in after 210 (217 or 227? - not sure, maybe neither and I just have a fixation on number 7, lol). I am sure that part of the heating is due to the winch which partially obstructs the lower radiator side. I also have the stock 1 row radiator, which definitely doesn't help too much either. This never happened once I went with the efan setup. And yes, the 3 10 inch fans are not the best option, if you have a heavy foot you'll still go pass 210 mark, but the main advantage is that at lower speed and rpm I still get about 3000 cfm of airflow, which I can't get with the viscous-efan stock setup.
Regarding stock fan air flow, the max is either 3600 either 4200, don't remember exactly, and this is in close to max rpm with the electric fan running (so both viscous and efan). 5600 cfm is the max of the viscous fan that I have (or had more exactly since I have now an 3600 cfm 16 inch efan) on the liberty Crd, and that viscous I think is around 19 inch with very aggressive pitch, this measured at around 4000 rpm, which will pretty much ruin the lil' 2.8 diesel puffer, so all this max cfm is useless in this case since nobody sane will drive with an engine close to redline.
I am not saying everybody should jump in the efan bandwagon, I am just saying that for me the efans work better than the stock setup. I am sure that there are better ways than this. Based on my research, the best 10 inch fans cfm wise are getting 900-1000 cfm, based on manufacturer specs. Those specs do not consider restrictions such as radiator, additional transmission cooler, etc. my calculations though, based on my cheap eBay 15 bucks anemometer gave me 1500 cfm for a fan with no restrictions, so the results are in line with what dirt bound offroad advertises for their efan conversion kit. Not sure why my numbers are so different vs fan manufacturer specs but I am sure I made the calculations correctly. Maybe the anemometer I used was inaccurate. Or, it can be because the manufacturer wants to play safe and under speced the fan, fearing being sued, etc. it would be great if the stock radiator would be taller and thicker, so it can get 2 14 inch fans. I think be cool has a twin efan setup for Cherokee with 12 inch efans that are rated at over 4000 cfm, but that requires some pulley mods or moving the radiator to the front.
Also, the viscous, thermostat and radiator were in perfectly functioning state when I noticed my temp going over 210 , so this slight overheat wasn't caused by a fault in the cooling system. Mileage wise, I one haven't noticed any improvements, as some would think, the stock viscous is I think too small to matter and I don't believe it can create a significant drag to the engine that would affect the mileage. Plus these Cherokees are huge wall lockers on wheels, with no aerodynamics. On the liberty diesel, I did gain about 1-2.5 mpg, depending on city/highway drive, but again that viscous fan is huge compared to the Cherokee's.
Once again, I am not arguing for the sake of argument, I mostly want to post my opinions and observations hoping it will help folks deciding what's best for them.