An easy thing to do here is we can compare it to what you get above the baseline from them.
For example, an Anaconda with an A7 shield has 595 shields baseline.
If you equip it with eight shield boosters, the maximum it can possibly carry, it goes up to 1547 for an increase of 160% shield HP. 20% per booster, not surprising. A tough customer, but also not terribly overwhelming.
If you pack its 6-4 slots with SCBs, by the time you exhaust all the charges your effective shield strength will be 7891, an increase of 1226%. That's spread across nine SCBs of various sizes, so it averages out to a 136% increase per SCB. Is a 136% increase in capability per module roughly what we should expect for "comparable" modules?
Ya ok....I don't see a problem with this...we are not talking about fighter jets here..these ships are larger than skyscrapers.