It is significant though?

The suggested board is powered by USB, that's 5V 500mA, so, 2.5W. Let's say the tube is run at the recommended 380V, at 2.5W, that's a current of 6.5mA, which is barely painful, and not dangerous. I guess that with that power, if the circuit really wanted to hurt you, it could boost the voltage in the 50-100V range for a ~30mA shock, which is definitely painful and the start of what is considered dangerous. Electric safety is complicated, there is so much to take into account: current, voltage, frequency, location, presence of water, etc... Skin resistance is far from constant.

Maybe it could do more if it disregards the 500mA USB limit to the full 1.2A that the Flipper Zero can deliver, or with capacitors, but it doesn't seem to have enough of them for a significant power reserve. If it could do that, I would also worry about plugging it to my Flipper Zero or to anything of value out of fear of damaging it, as it would have to be of pretty terrible design, but well, that's AliExpress after all.