It’s been said by various members that the positive effect of C Grip is targeting the muscles where it matters: the CC. Pushing blood is supposedly more productive through there than the CS (urethra), and presumably minimises risk of injury.
I use the basic OK grip for the most part. I try to use the C grip but that involves an overhand approach, which gets annoying after a few strokes imo.
Instead, I squeeze the sides by stretching my fingers out (palm facing the floor) and tucking thumb under hand. Using the sides of the index fingers, I just squeeze the CC and slowly move up. Because the only grip is vaguely from the index fingers, it can slip from the penis if it’s well lubed and too flaccid. I found it works better with a higher erection % and semi-dry/wet.
Another approach is like the above but instead squeezing with the webbed parts between thumb and index. The benefit is it can prevent slipping but, I believe, can twist the penis midway through the stroke because of how the hands overlap. Practice a bit on where the other hand is positioned to offset the twisting.