Hi, i visit this forum from time to time, if only to see some of the amazing set-ups. At the moment i don't keep fish, although 15+ years ago i did maintain a marine set-up.
I have never seen a blue-line trigger in person. Having Googled what they look like, they look a lot like the Undulated trigger, a fish i read about in books, a fish that was always described as 100% antisocial, should be kept alone, can be destructive towards tank equipment. It appeared to be a completely pointless fish to want to own.
Our local aquatic shop had an Undulated trigger for sale. He was quite large at about 5 to 6 inches. In the years i would visit the shop to buy food, salt etc, the Undulated trigger never sold (i moved area eventually).
The one trigger i did own, was the Picasso. I kept him with a Powder blue. Both were tiny when purchased. Picasso 1inch, Powder Blue 1.5inches. The pair got on very well, no fighting. Both grew and grew, and could be hand fed. I can totally recommend Picasso trigger's.