| again with the reptile sand. honestly i wouldnt use gravel for any pet (but fish), hermit crabs MAYBE even then i would be nervous tho
some benefits of the rep sand is that if they injest it, it wont harm them. infact many companies have added vitamins and minerals that can help aid your reptiles health. try sticking with natural colors. who knows what dyes really do to an animals health in the long run.
if a reptile were to injest a piece of gravel its likely to be fatal. if the creature is too small, they could choke, and/or could cut up vital digestive organs which can lead to death or a shortened lifetime of misery.
if the reptile is large enough not to choke on the gravel its likely that even the smallest piece can cause intestinal blockage (lethal if left untreated), and/or also cause damage, likely untreatable, to essential organs.
beardies also live in sandy areas naturally, where in the wild they may come across some pebbles but still would not live where as that would be the only substrate. even with the hard skins it could cause scratches and cuts that can be painful and if left untreated can become infected very easily. of course this can be lethal as well.
its not easy nor cheap to find an exotic vet that can save your lizard. | 
Similar Aquarium Fish Forum Threads 
I agree with KittieKat, go with the sand because gravel could hurt them.