Paying 5 mana for a 4/3 flyer is a deal made in limited heaven. On top of that, you gain at least 2 points of life when it enters the battlefield. So what's not to like?
Obviously, Aven Gagglemaster is not a bomb, but this cool bird can win the late-game by attacking through the air and keeping you alive.
Once again, this is a great card for Lifegain decks, though practically every white deck, including Azorius Control, will want at least one copy.