I've kept them... 5 of them to be specific.
My first pair I picked up I was able to get eating Ova after a day or two with a little help from my trainer fish, a yellow clown goby. Unfortunately after a week, one of them jumped, so I was down to 1. I never noticed any outright aggression, and they often liked to perch together. That could've been bonding or some sort of intimidation. That was in an 8 gallon nano.
A few months later the LFS got another one in, and despite being extremely emaciated I bought him. He did not survive the night, just too far gone.
My one guy did very well for a few months, but one day my wife decided to help me by cleaning the tank and she must have had some hand lotion residue. The next day my Jann's pipefish pair were both dead and the clingfish soon followed. My yellow clown goby was the only one who survied.
Here's an old video of my 8 gallon pre-poisoning.
A few moths after that I picked up another pair and they also went into the 8 gallon. One was eating immediately, no training required. The other was only picking a little bit and spitting the food out. I couldn't get him to eat and if he did pick at something it didn't stay down. Anyways, after a week or so he dissappeared. He didn't jump, probably died in the rockwork and was scavenged.
So I was back down to 1, but I had the one for a while, though I can't recall exactly how long. He eventually moved into a 58 gallon, then later to a 57 gallon. Shortly after the move to the 57 he too jumped.
One interesting thing about them is that they love to eat shrimp eggs. In the nano I had a group of 5 sexy shrimp and the clingfish would stalk them for their eggs. He would hover nearby, his head absolutely still while his body was doing that wavy swimming thing they do. Then he would start turning his head back and forth, sometimes upside down, often doing a barrel roll, trying to get into position. If he saw an opportunity, he would lunge forward (often upside down) and try to snatch an egg off the shrimps belly. When I moved to the 58 gallon I bought a group of saltwater ghost shrimp as a clean up crew, and also so I could watch the clingfish stalk them. Though to be honest, he kind of got lost in a tank that big.
I hope to someday get a group of 3 or 4 again for my 57, but the LFS that I bought them from is gone and I've never seen them anywhere else.