I use cuttlebones as well, never had problems with my fish. Some will nibble on them, but I don't think it'll hurt them. In fact, in my nursery where I have some snails and cuttle bone, the kids will nibble on them and it's a good source of calcium they need for their bones(especially their spines) which can be harder to get into baby fishies.
The only issue I had with them, was sometimes they can make the water murky for a short time. It usually clears up, but I didn't boil them or wash them first, so like another said, I'd suggest you either let them soak in hot water(I wouldn't suggest boiling...that may make them fall to pieces and you will want a chunk your snails can walk across to absorb it), or rinse them well in warm water. It may lessen that chance, though it was never bad, just kinda annoying and usually clears up after a day or two.