For what it's worth, I've never used either. Didn't give much thought to them. In my experience it was fairly rare to actually lose a Command Station to trigger a Shark event, because I'd never settle for anything other than "near instant AI wave annihilation", even on the hardest game I won (8.6 Mad Bomber, 8.6 Vicious Raider, 2x Waves, Showdown as only "faction", for reference).
In principle they sound good, much like a human'd exploit a temporary advantage this'd let the AI do that too, but as above it has to be overwhelmingly strong enough to kill the CS in the first place. Thinking it through, if the attack fleet is depleted after that, Shark lets the AI keep up pressure...if it's not depleted, it'll gain more power, take out another planet, gain more, etc...might lead to near instant death?
I'm not sure. I'd consider my opinion of low worth due to the lack of experience with it, but I think if they're...not incredibly hard to do, which I don't imagine, I'd go for it. I think they'd let the AI be more proactive against you/factions, rather than entirely reactive to what you do.
I could do a Classic game with them on, if there are other settings you'd like as well. Gives you more data.
EDIT: Checked in-game, and the Shark type that has the Exogalactic Attack says it also adds to the next Cross Planet Attack.