I have three different urchins in my 90. A purple pincushion, a Halloween urchin and another I don’t remember the name of. No algae in the tank but they attack nori sheets so they are easy to keep fed and healthy.
Also porcelain crabs are awesome. Won’t attack anything and filter feed with fans in front of their mouths.
Lastly, I haven’t personally had a reef lobster but was in my LFS yesterday when someone returned a 3” one that had started killing his fish. Had to remove all the rock to catch it. 3” was with claws, not just body. LFS guy said they have seen multiple that are model citizens and then multiple that get a taste for fish and take them while they are bedded down for the night. To me, not worth the risk.