The OB subs are very quick and will play up to 250Hz, they match planers, electrostatics etc in speed and dispersion. They also don't pressurize the room like a boxed cone. The room lets go of the note quicker and your ears don't get fatigued as easily. Kick drum sounds as real as it gets.

Down sides are minimal, no good place to mount the amp, they have to be 3' min from the back wall. They don't quite have the grip at 20Hz that a box based servo sub has. Danny usually augments his OB subs at the show with one 12" servo in a sealed box close to the listening seats. Wiring also needs to be done carefully as it can be slightly tricky if it's your first build.