How "safe"? Do you think that he can have an accident? ;)

It depends of you, your family, environment, etc.

I think that he is 15, testosterone is leaking from his ears. He can watch porn move in the Internet or create his own naked scenes. Internet porn sites offer nothing. Poser porn scenes let him learn 3D software and match (if he read BB tutorials). BTW I think that if young guy get foreign edition of porn magazine, can be good way to study another language ;)

Anyway - it depends of your customs.