I'm confused. Are you already networked between your three boxes? If so, can you already share files and printing?
Just looked at the Linksys site- I don't get it. You still need an external router for your DSL or cable modem. Looks like you might save a network card, but you might lose some control over the firewall to the box. If you already have a LAN and you still need an external modem, you already have everything you need except a firewall. If anything the box just saves the trouble of setting up the wall.
I've been to the mountain and didn't like what I saw.