I don't understand why people favor a cloak that only works while standing still. This will lead to overpowered campers and snipers. It would be much more useful the other way around: it should ONLY WORK WHILE MOVING, and you should become more visible when you slow down, and get fully visible when you stop moving.
Why? Because someone sneaking past enemies and getting to objectives and setting down drop uplinks is FAR more useful than an invisible camper or a sniper.
To balance it, you should not be able to hold a gun while cloaked, and any melee should disable the cloaking until a cooldown time has passed.

Invisible snipers and campers is NOT the way to go

I would like to add:

Cloaking should be an equipment module requiring a moderate amount of skills to use, and different grades of the cloak module (standard, advanced, and prototype) should have progressively better cloak duration, and levels of invisibility; for example standard cloak modules should only have 10 seconds of cloaking before the cool down, have a strong refraction effect that gives them away to those who pay attention, but the refraction effect should be much less in higher grade cloak modules, and prototype cloak modules would be able to be invisible for 20 seconds before having to cool down. There should also be different variants each with varying strong points and weaknesses.

Chevrons (the symbol over a player's head) should not appear on a cloaked player, even if his cloak is unconvincing visually.

Weapons (even knife) should not be usable at all until cloak is disabled. I don't mean once you fire or knife that the cloak turns off, I mean you can't fire or knife at all until you turn off the cloak, or until it has to cool down.

Cloak disabling should make a electrical discharge sound. This would give observant players a chance of spotting a newly de-cloaked enemy who is about to knife them in the back.

Cloaking should be meant for avoiding combat, not getting stealth kills.

There should be deployable equipment designed to locate enemies, and higher levels of this equipment should spot cloaked players at a certain proximity. I think there is an equipment listed in the store (though not currently in the game) that might fit this.

Cloak should be more easily fitted in a logistics dropsuit compared to other slot; they have lots of PG/CPU, and cloaking would be great for avoiding combat for the sake of supporting others (like sneaking past enemies to place a drop uplink).

Can't really think of more right now.