I read where Climo recommended the fork grip but never was able to visualize it. (I don't hold my fork like that.) Anyway, I've been through a few grips. I was using a three-finger grip (index-middle-ring) to throw drivers and the birdie grip for mid-range discs.
Thanks to the Climo vid you posted, tomjulio, I understand it now. I went out to a field today to try it out. It added about 50ft to my drives and more control over my mid-range/approach shots. The disc releases more smoothly and therefore has more spin. Where I was getting a little bit of wobble from the three-finger grip, the fan grip fits comfortably and there is no wobble. I've also reduced the power of my run-up and rely more on the hit to induce more spin on the disc rather than the velocity of my body.
I liked the three-finger grip and have been using it for about 1.5 years. It keeps the nose down much more than the four-finger power grip. The fan grip does a good job of positioning the nose down also. Using the three-finger grip, I found myself applying more pressure to my middle finger rather than on my index finger. It just didn't feel "right." The fan grip feels natural and my hand covers more of the disc which gives me more control.
If you want to add more spin to your disc, give the fan grip a try. Don't try to use your arm to add spin but instead focus on the release. You want more spin than velocity. Try pushing a disc through the air without spinning it.