There are several good reasons for wanting an external optical drive for your Mac.
If it’s a recent model, it is most unlikely to have an internal optical drive, nor any option for one: no current model of Mac even offers an internal optical drive as a third-party option. If yours had an internal drive which no longer works, then an external version is both cheaper and simpler, and may be the only way ahead when an official replacement is no longer available. A few users also like to have both an internal and an external drive, perhaps for easy duplication of disks.
Apple USB SuperDrive
For all the issues which I covered earlier, the Apple USB SuperDrive is quite a good buy, if your Macs can use it. But it turns out that this is not one model, but at least two, which behave rather differently. Early versions were described as the MacBook Air SuperDrive, as that is what they were originally intended for. However, there are two different versions of the MacBook Air SuperDrive: those manufactured prior to the autumn of 2010, with firmware versions 1CHQ or 2CH9, and those made afterwards.
On plugging my SuperDrive in, System Information doesn’t actually report a firmware version for it, but gives a version (2.00) and a serial number which starts with KZ2A. As neither of those resembles the old firmware versions, I presume that mine has newer firmware and should fall into the latter category.
The first (1CHQ or 2CH9) MacBook Air SuperDrives won’t work with USB-C Digital AV Multiport Adaptors, or the USB-C VGA Multiport Adaptor, and I suspect may have other lesser issues too. Later versions of the MacBook Air SuperDrive and its apparently identical replacement, the Apple USB SuperDrive, should work fine with USB-C adaptors, but they may include more than one firmware version which may have subtle differences.
These may explain why not everyone has an identical experience with their Apple USB SuperDrive.
Apple’s official statement on all its SuperDrives is that they should work with any Mac which was manufactured after 2008, not just models released after that date, except for those with a built-in optical drive. User experience is that if your model of Mac could accommodate an internal optical drive, even though it may not have had one fitted, then the external SuperDrive is unlikely to work unless you tinker with OS X as described.
Except that one user who has contacted me insists that his 2015 Apple USB SuperDrive does work fine with an iMac late 2009 27″ (iMac11,1 designation, I believe), and with a ‘unibody’ MacBook Pro from 2011 – both models which did ship with internal optical drives. So maybe there are other, more recent models of SuperDrive which are more liberal in their compatibility.
Third-party external optical drives
These are inevitably of variable quality, and do not all work as completely as an Apple-fitted internal drive, or the Apple USB SuperDrive. Users report a range of problems, from drives not working at all, to problems ejecting disks, and incompatibilities with iTunes and playing DVD video disks.
One model does seem to perform quite well and is worth singling out: Samsung’s SE208, recommended by @bramleycomputer. There have been some issues reported by users, but in the main they seem to be resolved by using the correct USB cable, a different USB cable, and/or updating the drive’s firmware. Shop around and you may be able to find this slimline drive for under £20, compared with Apple’s price of £65.
What was that about archiving?
One of the most fascinating subjects which has arisen when reading comments about optical drives is how few people seem to use them now. With the switch to streaming and online media services, I can see why few Mac users are interested in playing audio CDs or DVD video disks, although I wonder how people access their collections of movies on DVDs now if they don’t have optical drives.
What is much more puzzling is how anyone can archive completed projects without using optical media. There are alternatives, such as using old Time Machine backup drives, but for most users, I would have thought that optical disks were still the medium of choice. Perhaps not many people bother to archive any more?