Both work with the same concept, only one has room for krausen blow off, the other only c02. If the high krausen never makes it to the lid, they both work the same, if it does, then you'll be glad to have the blow off ready.
Personally I just use an airlock unless I see buildup nearly to the top, then I sanitize and plug in the blow off into a large cup, or jug of water. The reason I don't do this to begin with is because the airlock is easier and takes up less room.
On Deck: Chav Irish Red
Pipe Dreams: Chai Porter
Primary #1: Empty
Primary #2: Empty
Primary #3: Imperial Oatmeal Stout
Bottle Conditioning/Drinking: Brown Porter, Pale blonde session ale