I've found the 1640 with BSLB firmware to be a bit more universally glitch-free in use with various scanning programs in various installations.
The single biggest reason I choose to keep a 1640 in service for scanning is simple. A few years ago, people were concerned with a potential quality issue with Falcon DVD+R DLs judging by their own quality scans.
Fred Perez, the North American Falcon representative, not only sent samples of the discs back to the UAE for testing. He also had their technicians quality scan the discs with a BenQ DW1640 and Lite-on iHAS422, in addition to testing the discs with the highly accurate DVD CATS system commonly used for factory quality control.
In addition to learning that the disc problem was not a problem, this was their conclusion:
"We learned that the Liteon shows different results than the Benq when being used with Nero. As you will see by the attached graphs, the LiteOn shows significantly worse results than the Benq or DVD CATS's. This means that the Liteon is really not a good drive to use for media evaluation because it results are not consistent with Benq or the DVD CATS's."
Using the BenQ as a benchmark, the newer iHASx24 generation of drives is much more accurate than the iHASx22 generation. But as I have ready access to DW1640s, I go for the gold