There is another potential serious downside... if it's that efficient at absorbing energy, imagine trying to MOVE it. Movement is accomplished by adding energy to an object in the momentum category... if you try to move it, you're trying to add energy... which it absorbs. Yes, you can get it started, but it's acting like it's got lots more mass than the weight would indicate. Practically the classic "immovable object". Given enough, you can probably convert it to almost the classic "irresistible force".
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"You know how parents tell you everything's going to fine, but you know they're lying to make you feel better? Everything's going to be fine." - The Doctor
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"You know how parents tell you everything's going to fine, but you know they're lying to make you feel better? Everything's going to be fine." - The Doctor