I had one for about a year before I sold the tank and all its contents.
It did swim around in the day on occasion but not very often although I don't think it was all that active at night either. It could always be be seen though, sticking its head out of the rock. It did seem to leave smaller fish alone, but I've found all eels I've kept to be the same. They have poor vision and seem to relay on smell, and they can definitely detect stressed out fish. If a fish is dying the eel would find it quickly and eat it. If a fish was healthy, it was like it wasn't even there to the eel. Even feeding frozen was difficult as it took so long for the eel find it or grab it from tongs, but they could often catch live freshwater feeder fish.