Don't waste your money. I bought a half dozen fullbodies at the beginning, and I wish I wouldn't have wasted my money and just got the shells to begin with. I have 3 dozen shells now and they take up less space then the 6 fullbodies, easier to carry and have absolutely no difference when it comes to realism in the field. I use my shells 90% of the time over water 1'-3', and the other 10% is in the fields for my anual trip to ND. They are awesome in a water spread! I use them more then floaters! I still use sleeper fullbodies, because they do not make sleeper shells. I only us GHG, so I'm only speaking in regards their products. G&H or other manufacturers may not have the same realism in their shells compared to fullbodies, I'm not sure.
TIP...I've only found GHG Harvester shells at Macks PW. Cabelas and others (notsure about Roger's) sell by the dozen, meaning you have to by a dozen active and then a dozen feeder. At Macks, you can get a dozen with 6 active and 6 feeder. If you plan on buying more then a dozen, then I guess it really doesn't matter.
Full body ducks are great, but the realism in the shell is no different, plus the shells are cheaper, store easier and take up less space, easier to pack and carry in, and no need to purchase slotted bags for them.