Now that TLC 2 is out, these things are beasts. Their saddle is a smithy, they fly, they get weight reductions on METAL INGOTS and they can carry two dinos. harvesting a corpse gives them a buff that regenerates about 450 health over 20 seconds. A absolute must-have tame.
Getting a massive TLC update in March 2018. The saddle will act as a mobile smithy, Argentavis will be able to carry with Talons as well as with its beak, reduced carry weight on obsidian and a few other unannounced resources (similar to the mammoth and wood), and will also gain a Rapid HP Regen upon eating (likely from devouring corpses and not specifically food from inventory). Like so people can see!