The benq drives DO NOT correctly read C2 error information.
They will return C2 errors when the data is unreadable, but they will not return C2 errors when the data is readable.
To test this, you can draw a thin line on the data side of a test CD-R, straight from the inside of the disk to the outside of the disk. The disk should remain readable, but it will have a LOT of C2 errors. A good C2 scanner like the liteon CD-RW drives will show very high C2 error rates, but the benq drive won't detect any at all.