This is one of the oldest fish in the aquarium hobby. People had Paradise Fish in their aquariums in the late 1800’s.
One reason they were kept so long ago is that they can tolerate a wide range of temperatures. They can withstand being at 60-90F with no problems. I am pretty sure if you kept one at 60F all the time he wouldn’t be very happy compared to one at 75F.
I had a pair in my 55 gallon community tank and they didn’t bother any of the other fish. The female was getting chased by my Red-tail Shark and I suspect that she was injured at one point because she swam with her back end drooping, only propelling herself with her pectoral fins. I removed the Red-tail and she survived for months afterwards but eventually died.
I still have the male, and he hangs around at the surface of his tank, bothering no one and still relishing Mysis Shrimp and Brine Shrimp more than the flake food.
I almost forgot, the Paradise Fish can be trained to jump out of the water to eat! For a time, I had this male in a 10 gallon tank, with a glass top, and the water level down a few inches. I started by wetting my fingertip, sticking on a tiny bit of dry Mysis Shrimp and holding it close to the surface of the water. In just a few days I was holding my fingertip 2 inches out of the water and he would leap up and knock the shrimp off of my finger! There are Youtube videos that show Paradise Fish doing this.
The Paradise is commonly known to be an aggressive fish in some situations. Mine were not.