It is tough, because it has 15 hitpoints per kt!
You could spend 10kt of space on a standard armor, and get 40 hitpoints at max tech.
Or you could spend 10kt of space on your new armor, and get 150 hitpoints at max tech.
150 >> 40
Leaky armor is simply inert components without the armor ability, and which have a high number of hitpoints per KT.
Damage to internals is applied via a "hitpoints lottery" type system:
If you have 950 hp worth of leaky armor, and 50 hp worth of other internals, then (950/1000) 95% of the time, weapon damage will randomly pick an armor component to damage.
You can see how this provides excellent protection while still leaving a chance of damage leaking through to internals
For further details on the damage mechanics, bordering on the nitty gritty see:
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DEF 200 : Damage Theory
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DEF 340 : Armor Mechanics