Using a popping cork and a live shrimp can be a very productive combination. Popping corks come in many different sizes, shapes, colors and different kinds of noise mechanisms.
Cajun Thunder and the bayside paradise popper are the most popular but many other brands are out there that work just as well.
My personal preference is a yellow bayside paradise popper. The paradise popper is the most durable out of all of the "popping" style corks out there, because a titanium wire is used that will not kink or bend. The cajun thunder also has a wire but it is easily kinked or bent resulting in your cork not functioning properly.
The good thing about using these style corks is that you can use a variety of bait from natural to artificial but the combination of one of these popping style corks and a live shrimp is hard to beat when fishing for trout and redfish.
This type of rig is generally used in 6' of water or less. They are designed to cause a disturbance on the water surface that mimicks a fish feeding (popping noise) to get the attention of the fish in the area. When the fish come up to check our the commotion they see your shrimp helplessly dangling below.
I like to use about 12-24" (but 18" is a happy medium) of leader from my cork to my hook or jighead. Too long of a leader will have a negative effect on the "popping" noise made by your rig because it will be too far away from the commotion on the surface of the water.
When using a cajun thunder (or any other brand) give your rod a sharp, quick pull with the rod tip up about every 15-20 seconds. You can change the interval between "pops" to find exactly what is working best for that particular day.
All in all if you are flats fishing you should have a rod in your arsenal rigged with one of these corks on it, these can sometimes save the day if other ideas don't go as planned.