I had two hitchhiker mantis and a 1 pistol in the very first 25lbs of live rock i ever bought.
The big difference i found was the mantis click seemed to be three clicks in a row where as with my pistol it was one loud click. For a long time the mantis never harmed anything in my tank.....but after about a year i had some crabs and a pepperment shrimp go MIA. I had cut back on my feedings and i think thats when they started wanting more than frozen mysis.
Its something that i would personally keep an eye on and i hope that it is a pistol. Mantis Shrimp can be beautiful creatures and are highly intelligent and fast...but are nice in there own tank and not your reef.
Best of luck.