I have the slightly cheaper version of this, the MR3220 (150mbps wireless N vs 300 for the MR3420) and I can say it's a great device. Cheapest device with a USB port that you can run alternative router firmware on.
The biggest selling point for me is that it supports OpenWRT, though if you want to do anything useful with it, you need to install packages to external storage. I use this thing at my parents house to control the garage doors among other things. Also use it for active port forwarding when I'm on a natted network. But if you have this guy + a usb hub + a pen drive, the possibilities are endless.