They are reef safe, and eat floating plankton in the water- actually you have to feed by getting plankton like PE mysis into the water column. A deep sand bed is useful, but as mentioned not totally required, however you have to have some sand, not crushed coral. I had a few of them in a 4" deep sand bed, they burrow horizontally then. These eels are too thin to topple corals and they stay in their sand burrows 24/7, so they won't harm the reef- they prefer open regions instead
I will say they don't compete well for food, so you really have to get the food to them. Otherwise they're cool fish