They can be of help with some pests. Again it's always hit or miss. The good side is that if they won't eat the pest you got, they usually won't harm anything else. They also won't add much to your violins and are nice.
I keep a couple of leopards, a melanurus and a yellow cories which might eat pests. Also looking to add an anemones melagrides which might also eat some pests. Also got a couple of flashers, solorensis, lubocks and A long wish list of wrasses to be added.
the sixline might consume many pests but can get aggressive.