This is the OG old school bristleworm trap. I’ve used them for decades. They work. PERIOD. Even the big ones. Set it and drop it on at night near the spots you see an abundance of bristles and empty it the next morning.
It is 6” long so not too big. If you have bristles bothering corals you can stick this even vertical into the rock work and they will find their way in. Durable and worth the cost. Clear to see your catch