I performed the firmware update on a 16x Iomega Plextor and it worked beautifully. Requires you drop it into a PC to flash it - but after that you are all set. I replaced the DVD in my G4 with the Plextor and it has been the best dang CD-RW I have ever owned. I have trie dto make it fail and it just won't. You can't do that with just any Iomega though - only certain ones had the Plextor mechanism in them. Documentation indicated which models worked by identifying their numbers, etc. You can go here and get the instructions and the flasher - if you dare.
Be forewarned - as the docs say, don't do it unless you can afford to lose that drive, because if it goes wonky - your drives is hosed....no going back. Liek I said though - follow the direction exactly, identify that you have the proper drive and all should be well.