Two-section tripods are much longer than the 3-section models. Thus might not be as air travel friendly.
My usual tripod on journeys that demand air travel is the Sachtler ENG 2 CF. It is a 3-section carbon fibre model with 100 mm bowl and well capable of handling and supporting a 600 mm lens. I can squeeze it into my suitcase by removing the head. On the occasions where I had to bring the even more sturdy ENG 2 CF HD, the legs have to be split at the top bowl otherwise the unit will not fit inside the suitcase. Still no problem as these models are designed to be simple to take apart.