I've got a Manfrotto 190-series tripod with the horizontal arm, and I can attest to the utility and convenience of this arm design; however, I've found that using this arm just to flip the camera by 90 degrees isn't a typical use case. Most tripod heads can do this on their own, simply by laying the camera over on its side, and if you've got an Arca-compatible quick-release plate, you might want to look into an "L" bracket for your camera, which allows you to mount the camera in portrait orientation while the tripod head remains upright. Not only does this help keep the camera balanced above the tripod, it also lets you orient and pan the camera more naturally.
If you're interested in the flexibility of Manfrotto's arm design for macros, low-level shooting, and so on, though, I greatly prefer the horizontal arm to tripod designs that hang the center column upside-down, for instance. There are other tripod manufacturers that make "flippable" center arms, including Vanguard, which I've heard good things about.