I don't know if it adapted this stronger neck to deal with the predators on the Island, or if its lineage derives from before the stooped neck became common in carrion-eating birds.
Argentavis is actually slower than the Island's far more common Pteranodon, but it possesses significantly more stamina and can sustain flight for approximately three times as long. This makes Argentavis an excellent creature for traveling or hauling cargo over long distances.
Portable Hook-post: The Argentavis can be hooked onto using the Grappling Hook, making them useful for a number of tasks, such as taming from midair. Simply fly above the area you wish to tame a creature, dismount (make sure to equip a parachute or an Archaeopteryx!) and hook onto the Argentavis. Make sure it's set to follow you- it will move a little bit as you're falling, but when you hook on, it will stop; otherwise, it will try to land. (Level up Stamina and Health).
Egg Stealer: Wyverns or griffins are the best and secure options, but argentavis can be a good option for beginners players without the high resources and advanced mounts.