you can get one thats an exact fit for your car. the open element type is no good since it will be sucking in hot air from the engine area (unless you install a cold air intake hose).
the more obvious benefits are:
1. your car will breath easier since the filter is less restrictive
2. you'll never buy another filter. you just was and re oil it.
more hp???, that most probably not. even if (assuming) you make a 2-5 hp gain, you wont really feel it anyway. those 2 reasons above were good enough for me to install one in my car. i like it and my car loves it.
regards