I had a huge one(bout the size of a dollar bill) removed ASAP.
I did read further that the only ones that get this large, typically feed on LPS corals. Could explain why I lost a nice torch that was with me for a while before it just disappeared.
This type of polyclad typically feeds on snails but LPS is another possibility. Where there is 1 (or 2) there likely are many. I really don't know if flatworm exit is effective on them but I would guess yes.