Love this, 100% agree with your description of the 6 line. Constantly investigating every part of the tank!I have had one for about 6 years with no issues. He was in a 40 gallon cube, with 3 clowns, a file fish, and a watchman goby. He never caused any issues and I added the clowns and the file after the six line. I now am running a much larger tank, and am debating on when or if to add him. He's currently in a 20 gallon holding system, and may end up in my frag tank for some time. But I figure he's had 6 years to show aggression and hasn't so if he goes in the show tank it will be as the las fish in.
He is an amazing fish. I enjoy how he swims constantly, on the hunt for fod, and pops in and out of small openins in the rock. Great colors as well.