The answer is Yes ,Kali linux is the security distrubtion of linux , used by security professionals for pentesting , as any other OS like Windows , Mac os , It’s safe to use .

Is it legal to use Kali Linux?

Kali Linux is a open source operating system so it is completely legal. You can download iso file to install kali Linux in your system from kali linux official site its completely free . But use of it’s tool like wifi hacking, password hacking , and other kind of things.

Is Kali Linux trustworthy?

Kali Linux is good at what it does: acting as a platform for up to date security utilities. But in using Kali, it became painfully clear that there is a lack of friendly open source security tools and an even greater lack of good documentation for these tools.