How would it activate twice in one combat? It can't. You have to wait an hour before it can activate again. This precludes activating in the same combat. Unless you are just really burning to play out 1200 combat rounds. This gives some time to heal up between activations.
He said one mission, not one combat. You know, go to the place, whack some guys, get the info, follow the info to the mcguffin, whack some more guys, try to hand-off the mcguffin without Johnson boning you.
If the guy with the level 3 pump needs to ensure that the pump won't trigger again, there is a chemical that will neutralize the adrenaline release called MAO. It will keep him from overdosing and potentially dying. Or he can tranq himself to prevent activation in the first place.
There are no rules for that in SR4. Which is one of the many reasons why you have to change the AP to make it not crap.
Now, I wouldn't grab a rating 3 pump myself, but I can see those who might find it attractive. The most I'd grab would be a rating 2.
And that would cost you 1.5 points of Essence and a grip of cash in addition to making you take the equivalent of a gel round to the face every time you benefited from it.
Just pick up a drug habit. It's safer, cheaper and won't cost you a shred of essence until you burn out.
Besides, the stats it increases, like agility and reaction are easy enough to hit aug max for any build who might want a pump and has money and essence to burn. Strength too, but not too many people benefit heavily from strength. So, basically, what you end up with is a piece of gear which hurts you in exchange for a temporary willpower boost. Not a good look.