The -7 ability is like a mean extra turn spell that you play for the three players that are behind the one in the lead
Flumph provides a ton of card advantage if you can get your fellow players to attack it, as well as being a solid flying defender to keep your commander safe
It gives little ability to disrupt, no sneak peek previews as to what it is about to be inserted in your face and basically no response time
It's part Massacre Wurm, part Withengar Unbound, and it's an altogether cool addition to the set, even with clear multiplayer text tacked onto a Standard-legal card
That can be commanders that help you draw cards, provide ways for you to avoid being mana screwed, or just ones that keep the game moving and interesting
Kumena requires a lot more setup than Hakbal but becomes far more powerful once you've got the right board state