I signed up about a year ago. They send recipes to test....
about once a month. They don't mind if you don't test every recipe they send. Usually they give you 5 or 6 days to test the recipe and then give feedback. I have enjoyed doing it.
Most of the recipes are first concepts on shortcuts to more traditional recipes, improvements to traditional recipes, or just downright strange combinations. You are the guinea pig, and then they use your feedback to tweak the recipe. The tweaked recipe probably goes through several rounds of testers, who suggest their own changes.
Usually, the recipe that comes out in the magazine is far removed from the one you test -- or, sometimes, the recipe just doesn't get published.
Have fun!