There is a misconception that using a bone conduction headphone is safer than typical earbuds or headphones. With that said, it is also unfair to claim that bone conduction headphones are hazardous to the listener.
The technology itself is harmless, as proven by its use in medical aids. However, the nature of its usage may lead to hearing losses amongst users. While the bone conduction headphone bypasses the eardrum, audio sensory still involves the cochlea.
Hearing damages often occur when the cochlea is exposed to prolonged sound that is above a certain level. Excessive noise can also damage hearing nerves, which may lead to temporary or permanent hearing damages.
Like a conventional headphone, you shouldn’t increase the volume of the bone conduction headphone to an excessive level. The safety of using headphones, bone conduction or not, is ultimately dependent on the users.