The adapter works well when it works, providing full FireWire 800 performance. But users of the adapter have encountered a frustrating limitation: Only 7 watts of bus power is supplied to an attached device. The FireWire standard supports up to 45 watts, although most computers, including Macs, deliver 10 to 20 watts. Some bus-powered FireWire devices have an optional DC power port, even if they don’t include an AC power adapter. If you can externally power your device, you can bypass the 7-watt limitation. Otherwise you’ll need to explore other solutions.
Unfortunately, this transition seems to be taking a while. FireWire is on the way out. Thunderbolt devices are few and expensive. USB 3 is here and fast. It’s great in theory, but USB has never approached the reliability of FireWire.