The NI500 looks alright to me, and it has to be a bonus to have it external, I have 5 computers hooked up to my M1122 (with the help of an extra hub). They are a piece of cake to set up and 330 looks like a good price, I say go for it.
edit - oh yeah, do you know how many RJ45's it has at the back? If you want to hook up multiple PC's you better check that it can handle it. My one does DHCP and everything so I don't have to worry about it. Maybe if it only has one port you could just make a crossover and plug it into a hub if needed (?).