At first the FFE looks "what? that's op" until you read the small characters at bottom, its charge last only 5 turns.

For sure I understand it would be too OP without the limit, but at end I don't see any proper use cases:
- Nest missions don't fit that well. it's the first candidate that come to mind, and it would be for last phase, but 5 turns on 10 turns looks short, entrance tends be a mover forward not fitting the device to more static usage or at least slowdown a lot a move forward.
- Stop horde missions don't fit at all, either it's a lot of overwatch and then 5 turns means not much, either it's a move on strategy too mobile for the device.
- Derelict missions won't fit better as well, entrance and exit phases are to move forward most often and the FFE seems not fit well. And for 2nd part that is either kill em all or pick the data, I don't remind it would have been useful.
- Factions missions a bit like Derelict missions won't match better because of same reasons.
- The let missions in space and possibility of ship hull hole, but either you'll quickly learn take care with explosion to avoid create a hole in the hull, either alien explosion won't make such holes, or at reverse in the mission it's thematic but then there's multiple holes. Moreover for such usage it's clear that you put the device and lost it, so it's more a consumable then.

But I except some suggestions on good use cases.

Otherwise I can evoke design options:
- Allow recharge consuming some ammo/resources could be an option, but it's a delicate balance to find to stop the item being too OP.
- Gives it a limited amount of use, it creates the field force wall but stay in inventory, but it has a limited amount of charges as 2 or 3.
- Use 2 inventory slots, the FFE and a required controller to light it on/off from distance, and increase a bit charge duration, perhaps 7 turns.

But still waiting suggestions on when and how use it.