Furthermore, it's crystal, so using standard D&D logic, it probably wouldn't do well against sonic attacks.
On to the positives. Obviously, it's not metal, so effects keyed to metal (Heat Metal for example) wouldn't work on it, and certain effects that gain bonuses against metal wouldn't gain those bonuses. A kineticist firing an Electrical Energy Ray at the diamond armor-wearing BSF wouldn't get the +3 bonus.
You might also be able to argue that it could have some kind of ray deflection abilities.