I have always liked Plextor; I'm still using an old PX-32TS SCSI CD-ROM, a PX-R412C SCSI CD-Writer, a PX-W1210S SCSI CD-Rewriter, and a PX-712 ATAPI DVD-Rewriter, and none of these have ever given me any problems.
However, the PX716 is a huge mistake, in my opinion.
For starters, it won't read some software installation CDs (so I was highly fortunate to have access to a number of other units - none of which have any trouble reading these - or any other - discs); I actually have two PX-716 units, and they both have this problem. I upgraded the firmware on both drives from 1.04, through 1.05, 1.06, 1.07, up to 1.08 (the most recent version at this time), and after each upgrade, some existing problems were gone, but other ones got introduced. Neither of the units have ever really worked reliably.
Then, yesterday, one of the units broke down - it takes ages to recognise any disc, and even then, it won't read the disc until after a huge number of retries (if at all - I have just had it spinning on a disc for ten minutes !!! after which I gave up, and ejected the disc); the other unit instantly recognises the disc - at least, for now.
Sorry, Plextor - I'm done with you. I'm going to dump the PX-716 units, and replace them with something else - something that works, and that isn't so expensive. You will have a lot of convincing to do if you ever want to win me back as a customer.
I don't mind paying a premium for decent stuff from a company that I trust, but once they betray my trust, they can go to hell.