Lettuce Nudibranch?

This was ID on a Facebook page as being a lettuce nudibranch. And the photos seem to match up.




Are these guys good guys or bad guys. I noticed several as many as maybe a dozen most very tiny with the largest being 1/4 inch. I believe they rode in on a piece of live rock I got a few weeks ago. I have a FOWLR with one very small anemone that someone ID as a ball anemone. I would like to add like a bubble anemone or pulsing xenia or other easy corals. I kind like the little guys