Depends on what you mean by "safe".

Given the centralized nature of FB, there's a high chance that they'll be keeping tabs on all your transactions thanks to this crypto sharing data of all your movements (as well as your personal info) to a central entity, then I wouldn't consider this FB coin "safe" since I don't know what this company can do with all my info. If you think "safe" means a crypto created by one of the biggest companies in the world, therefore, they won't scam you, then yes, it can be considered safe.

We don't even know if it's going to be a regular cryptocurrency or a stable coin pegged to the US dollar, if it's the latter then you won't be able to invest in it.