Since router CPUS are relatively slow and uni core, expect 2 to 4 times performance gain if you were to use Hardware NAT.
Open source gives you freedom to shape your router any way you like. You can even do your own coding in C, BASH, LUA etc and make the router dance on your tune i.e if you know how to program. Even if you don't know programming, you can still use open source packages to customize your router any way you like.
HW nat as advertised by TPLINK may offer upto 800 Mbps throughput on WAN port. This could be useful if you have Gigabit internet connection. However for rest of the world who don't even have 100 Mbps internet connection (Including myself, most I get is 20Mbps), hardware NAT will offer no advantage. Yes it will reduce the load of your router's CPU but to do what? If you are using TPLINK firmware, you wont be able to do much with the CPU saving any way.
So in summary, HW nat would be helpful once Gigabit internet is commonly available and if router CPUs are pathetically slow. However HW nat can be substituted with faster multicore CPU (some companies have already started dual core routers) routers. I would prefer a faster CPU since I can do more than just NAT with it. The resistance to HW NAT seems to come from the fact that it does not fit the existing netfilter model. So I don't see any thing happening on the HW NAT side, unless the HW NAT would adjust to the existing software model or the need of speed forces programmers to change the netfilter model. I hope I was able to shed some light for you and others as well.
(Last edited by ron on 9 Jul 2013, 18:58)