I previously had dwarf puffers in a 29 gallon and yes they are notorious fin nippers and really shouldn't be housed in a community tank. I haven't noticed them fighting even during feeding. They actually just swim around together. I have seen them sleep near each other under the anubias (that is why there is now two anubias plants in the tank). I will keep an eye on them but as you can see from the picture their tank was where my temporary computer desk was set up. So I was looking or near the tank a lot. In fact the 5 ghost shrimp I added two weeks ago are still in the tank.
The blur in the picture is one of the puffers. I can get them both to follow my finger along the side of the tank to slow down for a picture but I thought my finger would ruin the picture. I'll try and get a picture of them together. Love puffers though, most character I have seen in a fish.