Just an observation that occurs to me when I see a reference to IB "vs" sealed: An IB
is a sealed sub (albeit one without an obvious "box"), in that it relies solely on the drivers for output and the back wave is isolated from the front. It has a large efficiency advantage (and less thermal compression) down low from the very large Vb, a typically very low Qtc, and no acoustic high-pass filter in the form of a stiff airspring behind the drivers. Also, since box size is not a restriction, IB-ers usually find it much more easy to incorporate large amounts of displacement, four 15's is fairly common. This has nice gains in dynamics and distortion as you might expect. I think this huge Vd is a large part of the epiphany many experience when they first fire up their IBs...a single 12 to four 15's is a bit of a jump.
The obvious disadvantage to me is the probable lack of placement freedom.