At $29, Apple’s new Thunderbolt to FireWire adapter is an essential accessory for the MacBook Pro with Retina Display, and MacBook Air models with a Thunderbolt port, even if you don’t regularly use FireWire devices. Why? Because it allows you to easily get to the files on your drive, using target disk mode, from another Mac, which can be essential if you are having boot problems, and simpler than using Ethernet if you are performing a migration.
And, if you are a MacBook Pro user with heavy FireWire needs, the adapter will give you an entirely separate, full bandwidth FireWire 800 bus.
The MacBook Air and MacBook Pro with Retina Display not only lack a FireWire port, but they also have proprietary SSD storage modules which can’t be easily removed and put into a drive enclosure for direct access (though Other World Computing sells a variety of enclosures for the SSD modules used in the 2010 and 2011 MacBook Airs). The Thunderbolt to FireWire adapter changes all that.
The only downside to the adapter is that you won’t be able to attach anything else to the Thunderbolt port while using it, including a monitor. On the MacBook Pro with Retina Display, this is less of a problem as it has two Thunderbolt ports, but it could be an issue for other MacBook Pro and Air users. Solutions to this include the Apple Thunderbolt Display, and the forthcoming Thunderbolt breakout docks from third parties.
Thunderbolt lets you have FireWire and Gigabit Ethernet for your MacBook Air
What’s the Difference between Thunderbolt and USB on the Mac?