I bought the Linksys WRT350N and it disconfigured itself, so I intalled DD-WRT Mega (first the specific mini, then the generic Mega, then HARD RESET), and it seems to be going fine. Hard reset is important, before that I couldn't get the wireless to work.
But it's not dual band. The 600N is dual band and it's also supported by DD-WRT. The 610N is not ready.
Of the additional things in the Mega, what I find interesting is the SIP gateway, but I haven't set it up yet. Maybe you just want to install Standard and save some flash for something else (you can also install optional packages in a USB drive).
You can use Firewall Builder on a computer to create the firewall rules graphically. Then you install the rules in the router. This is a normal Linux firewall. This is great, because the stock firewalls of some (all?) consumer routers are toys.