Finally here...
After some twists and turns with taobao shipping
Got it at about 270 + shipping during 618 promos. Consolidated shipping with some other stuff but I think was around 25 coz of the big box.
As the entire delivery came in a gunny sack (!), the box was quite dented as you can imagine, even the internal cardboard trays damaged, hope no internal injuries..... Got a free ASUS mouse pad, was hoping for the polo tshirt or bag
Since china set, power cable was china plug, so had to use an adapter.
Everything is in chinese (manuals and router interface), so i had to hunt for the English menus on the interface, even then some items are still in Chinese (there is some game fast vpn thing, which I think is for China region only?)
First thing it did was to auto update the firmware to the latest, quite smooth.
Other things that I did
1. turn off QoS, Smartconnect, set channel 44 for 5GHz with separate 5GHz SSID, turn on AiProtection. I think everything else was with default for now, other than the locale as mentioned below
2. reset AX3000, then use the router interface on it to set to AiMesh Node, then use the AX86U interface to link up, pretty smooth too, all steps guided from the Asus router web interface
Had some setup issues along the way after that setting up late last night, but seems ok now.
Previous setup : AX3000 + TP500 Extender
Now: AX86U router + AX3000 in AiMesh network, wireless backhaul
Setup issues
1. My old MBP from 2012 which I'm using for WFH couldn't connect to the router on 5GHz initially, until I changed the locale from CN to US then finally settled on Asia
2. On US locale, everything worked, but the speeds were really low on speedtest, much worse than in the previous setup. When I changed to Asia, much better, on par or slightly faster than previous setup
Initial thoughts
1. HDB 4rm flat, so I think alot of interference from other flats or my own stuff, I had to go back to my previous router settings of setting CH44 for 5GHz, else it was only 100-200Mbps avg on the iPhones (XR, Pro Max) next to the router (scared me at first)
2. Range seems to be the same with AX3000, i.e cannot reach MBR with stable connection. a bit disappointing but to be expected, given the limited area I can put the AX86U (punch through bomb shelter wall, and toilet walls/doors, so I still had to setup AiMesh to replace the extender network.
3. Really pleased with AiMesh, as now transfer of wifi from 86U to AX3000 is rather quick, takes only a few seconds. Previously walking in and out I had to manually switch from the router to the tp-link extender else connection will be very weak, or it would always connect to the further router/extender for some reason by default which was very irritating.
For now,
iPhone Pro Max - 700Mbps next to router, 300-600 on avg everywhere else
iPhone XR - 550Mbps next to router, 300-500 everywhere else
MBP 2012 a/b/g/n - 200Mbps next to router, 180 Mbps in MBR
Overall, quite happy with AiMesh, but I think maybe abit of overkill with AX86U for my use case, probably another AX3000 would be sufficient. There's a lot of gaming related stuff in the setups, but as my gaming now on the switch, and the games we play as long got connection can liao

. Speedwise only slight increase visible in speedtest.net, probably need some tweaking with advise from all of you, but I'm contented for now.
My NAS now only 1Gbps wired, so can't really take adv of the 2.5G also..