I would suggest sanding any rough or sharp edges off
i have afew pots and bricks that i have broken to give them a better more cave like shape. I always take tons of care to sand down any sharp and rough peices of pot after breaking them and wash them lots to ensure no dust or other unwanteds are still on the pot.
they give a cool effect, i have one of those pots with holes on the sides to allow a creeping plant to grow out of the sides of the pot. I took it and cracked the bottom off ( which will now be the top), used a grinder and made a cave-like entrance at the top ( which will now be the bottom) and sanded all the cracked areas, grinded bottom entrance and already made holes so that my puffs , plecs and corys cant hurt themselves.
i have yet to add it to my tank but it looks great already!