But then you have a blackbox and are forced to trust the manufacturer.
(And as the Snowden revelations show, you have to care about man-in-the-middle attacks over the postal system, while that blackbox is on the way to you.)
To add some tinfoil-hat mentality on top of that: I believe it is easier to manipulate a blackbox TRNG than it is to manipulate individual components (transistors, etc.).
So although the DIY approach has the downside that you may get things wrong, it has the upside that it is very hard to manipulate.
But then you have a blackbox and are forced to trust the manufacturer.
(And as the Snowden revelations show, you have to care about man-in-the-middle attacks over the postal system, while that blackbox is on the way to you.)
To add some tinfoil-hat mentality on top of that: I believe it is easier to manipulate a blackbox TRNG than it is to manipulate individual components (transistors, etc.).
So although the DIY approach has the downside that you may get things wrong, it has the upside that it is very hard to manipulate.