The best thing to do is read the FAQs on the cult website. They go into a lot of detail as to why an IB is superior, but I'll summarize.
Pros:
- 'cleanest' bass possible (sorry, but it is true- purity of bass can only happen in IB)
- Relatively low cost
- Low impact to room
Cons:
- Custom installation
- Less bass 'power' (at a given wattage)
- Time to implement
I read about it for a while, saw a couple of guys do theirs. When I finally got around to doing it, I was blown away. It is not 'rattle your teeth' bass (like the guys who have mono-frequency 'kickers' in their trunks) but dare I say... beautiful bass. And with the proper planning and design, it can kick your teeth in too- without the distortion.
People who have heard my system agree that it is the best bass they've heard.
Some info on mine on
http://farzanegan.org/ht (look for entries about IB)