They are acropora crabs... No harm having them on your sps... There are different colors and variants..
But if is this... CATCH it out... These eat acro...
It will not shatter your glass... The clicking sounds by the pistol shrimp is due to the quick snapping of its claw which sends jets of water that create the sound... Will not go into details... LOL...
The pistol will lose to the mantis...
Stumbled upon it while searching... Seems like another commersal shrimp with anenome... But it is found in cold water gauging from the countries they give...