A specialized networking card—with blingtastic LIGHTS—designed to murder lag for gamers, the $130 Killer Xeno Pro practically screams "snake oil." It's not quite.
If you've got a crappy ISP, obviously, a special thingamajig on your end won't help you—it can't fix the whole internet, and it doesn't claim to. What it claims is that network traffic running through it bypasses the Windows network stack, so it's a more direct connection to your game, and less load on your CPU, resulting in less lag and theoretically a higher framerate. Different from the older Killer cards, this also has a built-in voice processor to offload chat. You can customize network and bandwidth priority, app by app—giving your games the highest priority, obvs—so theoretically you can leave your torrents running and game normally.
Did it work? No and yes. I really didn't notice any difference in my framerates or latency playing Team Fortress 2. I keep the game's netgraph feature running by default, and I always play on the same server, so I have a pretty solid grip on what's typical of my machine in terms of framerate and latency. Playing 10 minutes on my standard connection and then switching immediately to the Killer Xeno for 10 minutes, and repeating this sequence three times, it was about the same every time—if it improved my connection or framerate, I couldn't taste it.
It does do a pretty decent job as a local QoS (quality of service) client. I ran a bunch of torrents and my game played perfectly okay, just like if I wasn't downloading a whole bunch of crap. However, if you've got a decent router, you could do the same thing if you know what you're doing. And really, router-level QoS is the only way to deal with your roommate's crazy torrent habits—the Killer Xeno Pro can't do anything about what the other people on your network are doing, so even then, its application is fairly limited.
Is it worth $130? If your computer's crappy enough, getting back that slight amount of overhead used by the Windows network stack and your usual chat client could make a difference. And if you can't figure out QoS, its software is pretty easy to use. But if your computer's that crappy, why are you spending $130 on a network card? [Killer Xeno Pro]