It's probably all just about the same. It says on my can use every 3k miles, so i just give it a little spray time to time. I'm not gonna say it's gonna make your belt last 100k miles but it should help them stay the best they can.

Most belts I believe are somewhere between 60-100k miles, although age and weather conditions im sure are added factors. Best to just visually check them when you open your hood. I just believe in preventive maintenance