Seems a ridiculously pedantic way to check a memory card, reading and writing every byte. H2testw ran for several hours testing my new 512GB card, and the progress meter showed only a few percent progress. It might have taken days, so I aborted the test. The test left about a hundred temporary files, which I had to delete. Windows 10 refused to format the card (can not format).
I'm afraid I can't recommend h2testw for large media. Does anyone know of a better utility for this purpose?
The point is that especially cheap and or fake USB/SD-Cards are extremely slow and report false sizes to the operating system. You have to write the complete media with data you can recognize later during read-back. To my knowledge hat's what they're doing: Fill the drive with specific patterns via normal file access. Nothing fancy. If you try to fill the drive with other data the speed will probably in the same ballpark like h2testw.
From what I've heard is that the wrong size will not cause a 'Disk-Full' error unexpectedly early, but by overwriting already stored data. Leading to notice that issue when it's too late. If you fill the data piece by piece the validation of the segments will say OK but the earlier data might be gone unnoticed.
By the way. The link to the developer to be sure you got unaltered files:
https://heise.de/-2859100 (it's German, but I'm sure you'll find it in the list of system tools there)