Black book claims to be the Facebook of the dark Web. Is it a legitimate/safe site (assuming that users don't divulge any personal details), or is it a feeder site for nefarious things like Pink Meth? Is there any way to tell how safe/secure an onion site is, or if it is a honeypot?
No. There is no way to tell. That's the characteristic of a hidden service, and an inconvenience sometimes. Like other onion services, you should use it with care, and at your own risk. In other words, if you are using Tor to conserve your anonymity, you should never trust such sites. If you only care about censorship circumvention, and anonymity is not a concern, it would not pose a problem for you.