LiteOn DVD drives are good for scanning DVDs, but don’t expect them to show the same error levels in general as your Plextor drives.
LiteOn DVD drives are not good for scanning CDs, since they only report C1 failures (E31) instead of all C1 errors (E11+E21+E31).
LiteOn CD-RW drives can be used for scanning CDs, but I’m not happy with the recent LiteOn CD-RW drives I have tested (5238S and 5239V) since they can fail to report any significant problem with deliberately damaged CDs. There are newer LiteOn CD-RW drives that I haven’t tested.
The A1 and A4 series are more or less similar in how they scan, but as always there can be significant differences between individual drives. The A3 series is somewhat different in how it scans, especially how it reports jitter.
Right now I’d prefer an A1 drive since it can report PIE, PIF and Jitter and also supports TA Jitter scans in CDSpeed. AFAIK the A4 series don’t support TA Jitter just yet, and it’s unclear if the A3 series will support TA Jitter scans.
Choosing useful scanning speeds is also a complicated matter with these drives it seems, and can depend on firmware versions and other factors.