I convinced a mantis to abandon ship by just dipping in regular tank SW
This is a topic on which there are differing opinions... Mine is that you shouldn't dip your LR
in anything odd when it arrives. It has had a hard journey and my #1 priority is to keep EVERYTHING alive. Unfortunately, that includes some things that you might regret having later.
For me, all the diverse life that comes on the LR
is exactly what I paid for...and that includes mantis and crabs and other things.
If you have an existing tank full of sensitive life already, then adding the rock directly in is great for the rock...but bad for the tank. If you have a tank that is mostly barren, just waiting for LR
..then get the LR
straight in there fast. Remove unwanted critters later.