So far so good. I just plugged it in. The MacBook Air recognized it, and considered it separate from my Apple adapter (which makes sense, as they should each have a unique MAC address). I then noticed that I was supposed to install a driver. Since the device was working, I decided not to. (I tried contacting Macally to find out what the driver actually did, and while they gave a prompt answer, it was confusing.) My guess is that you do need the driver if you’re running an earlier version of Mac OS X (or presumably Windows), and that the driver is still compatible with 10.5.
One reason to have a USB Ethernet adapter is for travel, when you can’t guarantee finding a WiFi signal. (Or for places like my office, where WiFi is not the internal network I need to access.) Unfortunately, the AIR2NET is a lot bigger than the Apple adapter. Fortunately, I have my choice of which to travel with.
On the other hand, it seems to run a little cooler than the Apple adapter. And it has flashing lights, which might be useful if there’s a problem.
Both devices only support 100 megabit Ethernet, and it’s not yet clear that it will make a difference in backup speed. (My other machines do backup a lot faster via Ethernet, but I’m not sure where the real delay lies.) But the device does seem to work as advertised