Ok, so I've been using it a day now. It's better than onboard NIC for sure, which isn't a surprise.
It also offloads networking from the CPU to the NPU, which helps about 3-9%, but nothing major.
I've also used the software to configure which program gets the most bandwidth, which helps when running uTorrent and a game simultaneously. You can prioritize bandwidth from 1 to 4, and uTorrent is now set to the lowest while browsers and games are set to the highest. I left Steam in the middle so it can get normal priority, but not over web browsing.
All in all, better than onboard NIC. Software which only works with the Killer NIC is the most useful part of the Killer NIC. CPU offloading is great, but impact minimal. Every little bit helps though.
Happy with purchase