I've just flipped through the forums a bit.
C1 and C2 errors are only relevant for CD media. The equivalent for DVD media is PIE and PIF.
The 1620/1625 do NOT report standard C2 pointers, which are required by audio extraction programs, so it is no better than many other drives in that respect.
However, the drive CAN report C2 errors in a non-standard way for the purpose of doing quality scans, which means that you can at least check the quality of a CD you've burned & get the overall picture.
[The drive can scan DVD media as long as the drive supports reading it. So DVD+R, -R, +RW, -RW, +R DL, and -ROM media should all scan fine.]
So for scanning, since it can tell you C1, C2 and jitter on CD media, it is useful. It is also useful for DVD media to tell you PIE, PIF, and jitter. As a CD ripper, the software would have to be configured to do extra software error checking since the drive won't tell the audio ripping software about some of its C2 errors...but you can know ahead of time if the drive will have any issue by doing a quality scan.
P.S.: you are TOTALLY allowed to link to outside sources when it comes to situations like this; it's harmless, relevant to the topic, and helpful.