I would definitely bolt/screw it down, but it should work just fine.
No safe - unless it's wired into a security system, and maybe not even then - is going to stop a prepared and determined thief. However, this one seems like it would present enough of a challenge to stop your basic crime-of-convenience burglar.
I actually have something very similar (in size and purpose), but it mounts inside the wall.
si vis pacem para bellum