The only benefit this offers, if offloading the Windows protocol stack to a different, dedicated CPU, saving your Host CPU a few cycles (unless of course the "NPU" is slower at this than Windows on your host processor). Unless your CPU is under a lot of load, it's not going to make any difference. The others here are also correct in that more of the latency in these online games is over the internet, which this will not help.
Furthermore, NICs such as your Intel, Marvell, Broadcom, and Realtek use Hardware Logic inside the chips, which is going to be faster than this 400Mhz processor running Software to do the same thing. The NIC takes ingress frames in, check the checksums in hardware logic, strips the frame off, and hands the packet to the protocol stack. On egress, it does pretty much the same in reverse (minus large send offload), all through HW logic.
Yes, this is a waste of money in my opinion as well. These days, on modern processors, at FULL line rate (1Gbs), most NICs consume less than 8% of your host CPU. At the rates in online gaming (generally less than 100K/sec), there will be no difference (especially when they're running other apps to control the thing, which it itself consumes CPU cycles at the host.)