"Elephant Feed" has the scientific name of Portulacaria afra, a succulent commonly used in bio-active terrariums for bearded dragon and other desert reptiles. It does not require much watering, but is slightly needier of water than most succulents. They should be treated as a non-toxic decorative.
Guacamole has had some in his "garden" for the past 3 months and is doing great. He doesn't eat much of the elephant feed, though, preferring to eat his normal fresh chopped veggies.
All beardie-safe cacti/succulents may severely change the consistency or frequency of your dragon's poop. As such, when you begin offering elephant feed it is important to monitor your dragon's feces to make sure they are not suffering any issues.
Please be VERY careful using "other succulents". MANY succulents and cacti are poisonous. Safe ones include Elephant Feed (Portulacaria afra), as discussed, many verities of Jade (Crassula ovata), and spineless species of Opuntia cactus (in particular Opuntia Danicolor) are all beardie safe.