No, the host isn't read-only, so if you have malware (which can see the VM and what its doing) you're fucked.

If you boot into tails, it's read-only.

That's the use case of Whonix.

http://whonix.org

Didn't know about this Physical Isolation feature[0] before. Does anyone have any idea how reliable this is?

[0]: https://www.whonix.org/wiki/Dev/Build_Documentation/Physical...

Only if you trust the host machine 100%. But you can never trust the host machine 100%.

If you did why would you be using TAILS?

For anonymity?