I'll guarentee you whoever sells you Lysmata wurdemanni as reef safe is lying to you. They eat what Matt sites from earlier. There are around 12 different species and only a couple of them are reef safe. Those are the true cleaners. The shy younger peppermint Lysmata just sit but as they get adjusted, they are active in mid afternoon on your coral polyps (they especially like to pull tentacles from montipora as they walk) and at night on everything soft. If you have lots of the monti's and like that behavior, maybe it will go unnoticed? If you have tubastreas, anemones and soft animals to spare, go for it. Maybe those large BTAs will be able to grow back fast enough that you won't notice the damage for a while, or did you sell them?
Lysmata adults make good plankton producers for a special refugium that feeds into the main tank. They can have from 800 to 1200 larval shrimp every 14 days if fed well. They will also eat all the feather caulerpa in there if you have any. Its actually kinda surprising to me every time reefers want to add these shrimp to their tanks these days with all the documentation that says they are not reef safe. Since I had the benefit of being home 24/7 to observe and to breed several varieties of shrimp, I got to see the ____ in action. I stripped my reef to bare bottom to get them out after high losses as sited by Matt. Lots of luck to all who go the same path. Ask Jenn, she posted her sad story of them eating all kinds of stuff on here some time ago too. It must still be in the messages somewhere as have others.
The price is your clue that they come from jetties in masses. Just cause you don't catch them yourself doens't mean thats not where they come from. You get what you pay for and cheep can spell disaster. Ask GaryP, he posted that exact same statement a while back as well.