Set aside who designed the amp and look at it from a design standpoint. I’m not an EE but have built about 22 tube amps and repaired many others, and have built and repaired a lot of solid state gear. I rely on current information on safety from books and qualified engineers either in person or online.
First, as has been said before, proper installation of the fuse is in the hot (line) leg of the primary winding of the transformer along with the power switch. In years past, the neutral was fused but this is incorrect because it could blow, leaving the hot connected to the circuit through the switch, waiting to complete a circuit through the operator or internal mechanical failure. This is a strange holdover from early tube amplifier and radio designs that I’ve run across, and it gets replicated to this day, which is incorrect.
Second, I don’t see how the unit can be classified as Class II, where it is double-insulated. Even if it had a completely non-conductive outer shell, the circuit, which is connected to the chassis per the schematic cited earlier, could be connected through the input/output jacks, exposed screws, etc. That means the unit should have a safety ground connection - a dedicated, short piece of green or green/yellow wire connecting the ground lug on the IEC jack directly to a dedicated nut/bolt through the chassis.
This is so that if any hot part of the wiring comes into contact with the chassis, it will blow the fuse and/or the service panel breaker. In the US, neutral is tied to the ground buss bar in the service panel, so hot leaking or making direct connection to neutral or ground trips the safety devices.
Some manufacturers consider the transformer to be a safe isolation between AC wall power and the circuit and chassis, but that does not account for a potential failure at the primary side of the transformer, or the transformer itself which could short internally (some output tube failures can cause this), coupling the circuit with AC and the chassis.
Hard to tell from the photo, but if I read the comments properly, the rectifier board is glued to the chassis? If that is correct, it’s really bad design/construction. That is a high voltage part of the circuit with lots of current and should be very well attached to the chassis.
It will be very interesting to hear what the company provides in response to the questions by the OP!