The admirals with black globes are like a dog with a squeaky toy. None of them know how it works but they all know they want one. With a black globe generator a ship or installation becomes invulnerable ... for a while. Energy is absorbed from the hull of your ship where it can make huge holes and diverted to your jump capacitors. All forms of generator don't require any appreciable power. As a bonus it provides stealth in space.
The drawbacks are that the protected ship can't see out or maneuver while the globe is on. You could flicker the globe to provide partial protection but this affects your fire as well. This is pretty bizarre as even TL 4-5 biplane designers figured out how to fire machineguns between the blades of their propellers.
In theory a Scout Courier could mount the same one that a million ton dreadnought does. Note that the dreadnought has a lot more jump capacitors than a dinky Scout and could probably weather the explosion of planet Krypton while the Scout will probably give up the ghost to the communications laser array from the dreadnought (dreadnought commanders like to shout when they make their ultimatums.)
Black globes are usually found in extremely old alien ruins where they oddly are found still working correctly. Alien tech is like that. It either works right from go or does nothing. It rarely sends you the wrong way down a one way street or drops your phone calls.
That part about one size fits all is intriguing. How big can you make a black globe? Could a Scout ship extend it and its effects to a flotilla of fighters? For that matter you could fire a bunch of remote controlled nukes from your fleet, have them maneuver close to a control ship and have them all invisible in the globe as they coast to your target. This could usher a new age of planetary bombardment for one thing. The defenders are on a planet which probably doesn't have a maneuver drive or any agility to speak of so the coasting is not a significant disadvantage.
A black globe also is ideal for pirates. Cruise in close to the unarmed free trader you want to loot. Hit the globe isolating you and your prey and proceed to loot. Let's see Free Trader Beowulf yell for help then!
Use your black globe to give your opponents a surprise. Have your dinky lead ship jump into a star system and then throw the shields on. Then have the rest of your fleet emerge from jump space inside the globe. Drop the globe and hilarity ensues. I'll also note that you never know what forces are stationed at an installation with a globe. That big black marble might host an x-boat with mail and cookies or a battlecruiser squadron. It's sort of like playing the shell game only with spinal mounts and nukes!
It's pretty obvious from the description that missiles can't penetrate a globe in any meaningful way. There's no sailing through the black and then exploding. Could you use a black globe equipped ship to ram? Possibly. You would probably have to divert some energy into your capacitors and it's the referee's call whether the other ship would be messed up enough to justify your capacitors filling up.
This point becomes moot if your black globe is hiding a kilometer wide asteroid you've aimed at your enemy's home world. It's ironic that a magical piece of alien technology that was fabricated when mankind was living in caves would be turned to hiding what was the caveman's first ranged weapon: a huge rock.