you misread me / I let myself be misunderstood by writing too hastily.
AOpen 1648/AAP IS consistent from scan to scan (same disc). This combined with the fact that it reports read errors within specifications and that it's read error counts are more in-line with Pioneer/BenQ/Nec/Plextor (than say LiteOn), makes it a very trustworthy read error tester.
But it is not always consistent with LiteOn or Plextor or BenQ or Nec or Pioneer.
But there is not a single consumer drive that is always consistent with scans from every other drive (this excludes Pulstec calibrated industrial drives).
It's just not possible, due to how focus error, tracking error and slicer level implementation varies from drive to drive (different puh, firmware, mechanics).
You must understand that no two drives will always scan alike.
DVD-1648/AAP is consistent from scan to scan using the same disc.
It results just don't always agree (and don't need to!) with other drives.
I know this, because I've tested all of the above. And so has Erik D (CD DVD Speed author) and he tends to agree.
So, please let not propagate the overgeneralised myth that all dvd-rom drives are unreliable.
Mediatek chipset based ones are unreliable (I've tested half a dozen of them) as are some Via based ones.
But AOPen DVD-1648/AAP is not one of them.