Unless they are riding in some extreme conditions , i do not see any need for a Oil Cooler under "normal" conditions , the fan on the radiator ,yes , i have one , its a must if you ride slow single track , or for street use , but a good quality synthetic oil will help more than a oil cooler as far as i am concerned , if the oil is getting hot enough for a oil cooler to be needed , then your engine is overheating anyway , and i would be more worried about blowing a head gasket before i would be about cooking the oil itself , the temperature for oil to turn to a varnish is much higher than the temp would be to blow a head gasket , so the chances of the oil breaking down from heat are pretty much non existent , if your worried about cooling the engine , run a Radiator Fan like this one
https://www.crfsonly.com/catalog/produc ... ts_id/5360 and Engine Ice coolant , or Evans Waterless Coolant , all that combined is 1/3rd of what that oil cooler cost and the fan will be more effective
The place you want more oil is in the transmission side , the engine side does not really need it , most of us run 1 full quart in the transmission of our R's and X's , but the recommended amount in the engine side