The LaCie Ethernet Disk mini is the first NAS I've tested that can be either an NAS or a USB external drive. It's a nice capability that gives consumers the flexibility to share the drive across the network, or for higher performance, plug it directly into a USB 2.0 port. This flexibility appears to cause a trade-off in performance, however, most likely due to the use of the FAT32 filesystem that provides compatibility across modes and client operating systems.
The mini isn't the fastest consumer-level NAS I've tested, and it has a lot fewer features than others, especially when it comes to configuring shares. But its cross-platform compatibility and dual personality might outweigh those negatives and make it the right solution for you.