It’s asking like “how secure is it” / “is it secure”?
Whonix was founded 7 years ago. Therefore tons of things were written on this subject. You can find a lot information on this subject on whonix.org as from many third party resources. Therefore won’t rehash the question here since it’s a too unspecific question.
This link may be answering your question more directly:
This documentation is a crash course in anonymity and security on the Internet. Whonix ™ is a technological means to anonymity, but staying safe necessitates complete behavioral change; it is a complex problem without an easy solution. The more you know, the safer you can be.
Since Whonix is Open Source / Freedom Software, the source code and extensive documentation about everything that Whonix implements is available in public and for free.
What I’m wondering is – does Whonix act like a tunnel? Is it similar to a VPN?
When data is being transmitted from Whonix to the Internet, can that data be monitored by someone near the WiFi router? In other words, is it possible for people to eavesdrop on a Whonix connection, and see what websites the Whonix user is visiting?
Also, will adding a VPN on the host computer improve anonymity?