The technical documentation claims stuff like that it disables bad sector allocation. That's actually a thing, but if you read the man page for some reputable software like hdparm you'll see a nice little note:
> Control of this feature via the -D option is not supported for most modern drives since ATA-4; thus this command may fail.
ATA-4 was standardized in 1998. It can probably actually disable write caching, but it's not like that's unique to SpinRite in the slightest. It's even trivial to change that on Windows which is otherwise horrible for anything low level involving disks. SpinRite doesn't even use LBA48 addressing so if your drive can't address the full capacity in ye olde CHS then too bad, but SpinRite will try to spin that as a problem with your BIOS, a problem with your SATA controller, etc.
I don't see why anyone respects anything he says given his long history of selling snake oil and other shyster tactics. Even the Wikipedia page for SpinRite looks astroturfed and the talk section has a bunch of responses from an unregistered user that all seem to have a similar tone and be suspiciously supportive of some of SpinRite's dubious claims.
If Steve Gibson told me that the sky was blue I think I'd have to go outside and check.