Harley Davidson and Lenale Engineering both make fans that mount on the left side of the engine and blow air from the left side across the heads. Such fans are usually recommended for bikes that are involved in parade duties. The HD version is larger in diameter than the Lenale version and looks more like a fan than the Lenale version.
I've had the Lenale version for several months. It was easy to install since it plugs into the accessory plug under the seat of my 09 Road Glide. It is hard to say if it makes any difference but I'm a little paranoid about overheating since I come from the water-cooled world. I usually turn on the fan when I'm stopped or moving slowly in heavy traffic. I haven't checked the oil temperature before and after turning it on. Several of my fellow riders made fun of the fan but all wanted to know where I got it after we were stopped in heavy traffic and they began to worry about their oil temperature.
I know that Smitty had trouble with his Lenale - I think it shorted out and caught fire. I haven't had any trouble with mine but I always keep an eye on it. Between the fan and the oil cooler and full synthetic oil, I've done all I can to keep the oil temperature as low as possible. if nothing else, it gave me some peace of mind on my trip to Sturgis this year when I rode through slow traffic in Las Vegas when it was 112 degrees.