Fort Knox makes some very good gun safes, they have many perks that make them nice. Though they are not necessarily more secure than other safes, nor are they necessarily equipped with any better fire protection than other safes. They do, however, tend to have a much nicer paint, a much nicer fit, and a stellar finish in comparison to some other safes. They also allow some other design elements that add to the cost, however, many of these do not generally add to the protection. You can get thicker steel or double wall steel bodies as an upgrade, you can also get a heavier plate steel inside the door, adding more fire protection.
You can also get left-handed or right-handed hinges, as well as internal or external hinges as upgrades too. Fort Knox is also American made, which can be an important factor to many buyers as well.
Whether they are necessarily good is unquestionable. But, it's hard to say if they are definitely at the top of their game, it is probably safer to say that they are on par with many of the other top-notch popular safes out there.