RAW: Reusable. It isn't listed as one use only.
This game is narritive and there are things that seem weird because of this. The game design is that you don't need to track the small stuff. That's why there are no rules for buying ammo (other than in-combat reloads), restocking medical supplies, food, fuel, ect.
If you want to put some limitation on the Extra Reloads, then the house rule my group went with was one use per combat encounter. That way you can make someone with Extra Reloads run out of ammo by giving them the same result twice.
No argument on the RAW, but medical supplies--namely stimpacks--do need to be restocked. To some it may seem odd that stimpacks are treated one way and ammo packs are treated another.
As far as the limitation you mention, it's a good suggestion.
Energy weapons can be recharged easily. most likely on the characters ship. The chemicals in a stimpack...not so much.