Inky, I thought I was reasonably familiar with just about every diet plan out there, but I've never heard of the Greysheet Community. I don't think anyone in our group is following that plan because we all talk about what we're eating and that certainly doesn't sound like a plan any of the maintainers are following.
When we've surveyed our maintainers about which plans worked for them, the hands down winners were calorie counting and "my own plan". Not many of our members lost the weight and keep it off on a name brand diet. Like Glory said, in order to make it a lifestyle and not gain the weight back, your eating plan needs to be something that you can stick with for the rest of your life. And that means it will probably look different than anyone else's eating plan.
If the Greysheet Community is something that you can picture yourself following for the rest of your life, then it may be the right plan for you. Best of luck for continued success!