I had one in my 30 when I was first starting out in the hobby. It lasted about 6 months. Then one day it was upside down and covered in nassarius snails. For what it's worth, it did a good job on algae while I had it.
Helpful and very effective for green filamentous algae. Very vunerable to predation, shrimps, most fish and some corals will even try to get a piece of them (I found mine partially digested by my fungia plate coral).
i just bought one to help out in my dads 90. seems to chowing down like crazy but ive heard the same about their lifespan. They dont seem to last long (few months).
Cute little urchins...especially when they are wearign your zoos or whatever else they can find and stick on themselves! If you don't mind that or that they are a little clumsy with mknocking corals over-they are great tank cleaners!