Oh, ok. We're discussing brands and not technologies. Cause on the technology side was gonna say to prefer Thunderbolt-Ethernet over any USB-Ethernet alternative. Especially if you want performance and can snag a Gigabit connection.
Pricewise, we know that Apple is a computer maker, not a network gear fabricator. So the dongle sold with the fruit on the label was made for Apple and you're paying an extra for that fact. Question now becomes who makes the dongle and whether they can and do sell the same with their own label.
Or you can say "the heck with it", purchase the Apple dongle and be done. After all, it's not like you'll be doing that again till the one you got falls apart. How much do you expect to save over the regular $29 bucks?
http://store.apple.com/us/product/MD463ZM/A/thunderbolt-to-gigabit-ethernet-adap ter?fnode=51