A USB 2.0 Ethernet adapter is a pitiful thing, an ugly workaround only really useful when you find yourself in a Wi-Fi-free hotel room with only your MacBook Air for company.
A USB 3.0 Gigabit Ethernet adapter, on the other hand, is every bit as good as having a real 10/1000 network connector hole in the side of your machine.
Better still, as this uses a USB 3.0 port, it won’t clog up your Thunderbolt port, leaving it free for all those cheap and plentiful accessories that have flooded the market (note, that was sarcasm). And yes, a passthrough Thunderbolt/Ethernet adapter would surely be a wonderful thing, but it probably wouldn’t cost just $55.
If you need such a dongle, then you probably already bought StarTech’s little box as soon as you saw this post. In fact, the only downside seems to be that it looks just like one of those phone-line filters that come with ADSL internet packs. Try not to get them mixed up, or it’ll be a sad, porn-free hotel stay for you.