hm.. well it depends on first the rest of your team, like do you have and other Pokemon that could use the Z move boost? Also, it depends on your Tapu Koko's stats. You see, if you do want to use it's Z move to deal with bulky Pokemon like Snorlax, then it's a semi good choice. It does get rid of some tanks, but the Life Orb has the same effects (sort of). And besides the Z move is a one per battle thing, while the Life Orb lasts throughout the battle. And I ,myself, wouldn't use the Tapu's. My prefered legend in SM would be Necrosma. It's SP.ATTACK is very high, it can take a hit from it's disadvantages, and it's relatively fast. You can use Tapu Koko to take out tanks, but in my experience, most tank Pokemon have horrible SP.DEFENSE (except for Toxapex) so I would recommend you replace Tapu Koko with Necrozma. But the choice is completely up to you. And if you do some comparisons, the Tapu's pale compared to Necrozma.