Opinions and reviews on the FLH oil coolers.
 

Absolutely none are worth anything unless mounted in the wind, and then they do very little as measured in efficiency.(Measuring temp in and temp out)
Most stick them behind the front fender in the shadow of air flow.
No good.
Oil is not a very good medium for cooling as it takes a lot of it to do it ...but if you do it right is will help a little.
I mounted mine outside of dwn tube and on the bottom of the crash bar.
It is hardly noticeable

The other things to consider with oil cooling is line size and the boundary layer of oil inside.
1/4 and 3/8 inch line is almost useless once the boundary layer sets up inhibiting oil flow and the thermal conductivity.
I think it would be more efficient to have an oil cooler on each side if you really want to dissipate heat.
The boundary layer would be less restrictive for one thing and two coolers has to be more area to exchange then one .

Looks like a copy of ultra cooler that I have. Makes a big difference even behind the tire.

What you said about a cooler being in the wind makes a lot of sense. I picked up a set of coolers from an Aprila 1000 and I'm working out a way to reliably mount them inside my engine guards. Lots of wind and they will not impede air flow over the motor.

The biggest challenge is going to be how to mount them securely so they don't fall off, and yet look good enough and not like some hayseed hack didn't cobble them onto the bike.

https://cimg4.ibsrv.net/gimg/www.hdf...087ade91c8.jpg

If you want to do some experimenting?
Take clear hose the larger diameter the better.
You fasten it where you think, is a good place for the cooler.
It is aimed into the wind.
the angle is important to remember as your cooler needs to represent that in the end. (horizontal is probably best)
Make sure it comes horizontally l back a couple inches and whatever you choose for that distance remember it.
as you will repeat this a couple times.
After it comes back a couple inches put a downward "U" in it like what is under your sink.
This "U" will go dwn about 6 inches then back up.
Fill the "U" with food coloring.
Put some numbers about every 1/2 inch up the "U"
Go for a ride monitor the results of how hight the water is pushed at the different location where you might put the cooler.
The higher the number the H2O is pushed, the better the place for you cooler as that represents the best airflow.
Use a speed that is you avg for you, as that will also change the known pressure areas.

My 02 oil temp dropped 15 to 20 degrees with a HD cooler.....

Hd cooler
 

You can get a 10 deg drop just running the oil through the crash bar.
But is it a bit of work to clean it all out correctly so you do not destroy the engine with FOD.