pros: power efficient, good sq, usually plays notes down to the next octave of tuning
cons: huge enclosure, limited power handling, only certain speakers will work in them
They are not always huge and to say they have "limited power handling" is deceiving as transmission lines can offer just as much, and more, cone control when compared to sealed and ported boxes. People try to compare their power handling to an IB situation and that is not the case at all as there will be significant pressure build up behind the cone around resonance, similar to ported enclosures.