The Yellow Machine's RAID features can bring a greater degree of confidence in the safety of your data than you might find in an inexpensive consumer NAS device. In addition, the flexibility of its built-in switch and router bring extra capabilities to the table in a compact form-factor.
But the Yellow Machine misses the mark on a number of points, especially its primary value-proposition of being an all-in-one box for small-office users. If all you want is a basic NAT firewall, the Yellow Machine will probably suit you. But its use of a proxy that is limited only to email and web protection (and buggy at that) will give you fits if you want to limit what users can do on the Internet. Frankly, you'd be a lot better served buying a $40 router and just setting the Yellow Machine to Storage mode.
But even as a NAS, the Yellow Machine fails to match up to RAID competion like Buffalo's TeraStation and Infrant's ReadyNAS due to its missing print server, inability to connect to USB-based storage devices and missing support of user file access via FTP and HTTP.
The bottom line is that the Yellow Machine's relatively high cost, merely modest performance, and problematic proxy behaviors should cause prospective purchasers to think twice before buying.