In an over-crowded marketplace, ya gotta have a gimmick to make your product stand out. And in the world of "keychain" or "flash key" style 802.11g USB 2.0 adapters, things are no different.
Buffalo's product is the first time I've seen an adapter in any format that carries and auto-installs its own drivers. But depending on your needs or preferences, other differentiators such as the soft-AP feature in ZyXEL's ZyAIR G-220, flexible connector approach taken by 3COM's CRWE254G72 and IOGEAR's GWU513, or flexible connector plus flip-up antenna feature offered by the Linksys WUSB54GP may be more attractive.
In the end, despite its little quirks, Buffalo's WLI-U2-KG54-AI delivers what it promises. So if the idea of having a compact wireless adapter that can be kept in your pocket and installed on any Windows machine without having to carry driver installation disks with you strikes your fancy, then give it a shot.