When ordering from Amazon, there is a lot of trash to be honest. It's possible that you get a device that just uses a rand() C function on a microcontroller or something.
Worst-case even just spitting out numbers deterministically and not uniformly random.
Well, to be fair, I was talking about
legitimate usb devices. Unlike say the flash drive market where fakes are all over the place I don't think that's the case for this type of device and the reason is simple. The market is small.
That's why I'd prefer to buy a device with open-source hardware.
then why not get the onerng.
https://onerng.info/ you got something against it? seem like it checks off all your boxes. i doubt anything else comes close.
Trezor and Foundation Devices have shown that open-source hardware is possible without your business going down due to the bad bad DIY scene.
never heard of foundation devices before you mentioned them. but i'd say these are the exception rather than the rule. then you have to ask yourself, why.
So: As has been said, you must understand the hardware and software used to produce the number. A difficult task. Many have written words to the effect: Don't try to generate a random number on your own. It is extremely difficult. When your number is not random, you won't know it until your coins are gone.
why would it be "extremely difficult"? give me a pen and paper, i'll write down a string of 1s and 0s of length 256. i bet no one ever came up with that private key before.