EU firmware have the usual 2.4G channels and only 4 5G channels namely 36, 40, 44 and 48.

US firmware have additional 5 5G channels which are 149, 153, 157, 161 and 165.

If you plan to use 5G as backhaul in WDS mode and also for SSID wifi broadcast, then i recommend flashing to US firmware. However do take note that 2.4G wifi signal is much weaker than 5G signal. If you have other device that need to connect to 2.4G signal, then i suggest you remain with EU firmware.

Which US firmware? This one? https://www.tp-link.com/us/support/download...00/v1/#Firmware

I am using different method to set the wifi country code for EU firmware via config.bin method. It works. 
I leave the EU firmware default country code for 2.4ghz wifi while editing the 5.0ghz country code to US. The best of both world. Impressively, there is really an increase in 5.0ghz signal strength dbm.    Not sure if the increase is caused by beamforming functionality.

This is because US FCC allowed higher txpower. Btw, how to edit the config.bin?

Most high-end phones in the market can deliver up to 800mw, so don't worry about the receiver. As for the speed u got, it's normal since this C1200 is 2x2 MIMO device, real world speed for 2x2 devices is about 500~600mbps max, if u can get wi-fi speed about 320mbps at the place, and u put C1200 there as an WDS, the speed will cut into half, half to talk to the main router and half to talk to ur phone. I plug a LAN cable to my PC and set this C1200 as 5G WDS, the speed I got is about 500mbps, if I connect my phone to this unit I got about 250mbps.

The best way to use this C1200's strong 5G is to set it as an AP, it has 802.11k supported so ur devices which has 802.11k supported will experience seamless roaming between any router and this AP.

Btw, forget about MU-MIMO, it's almost useless, just marketing

I can confirm @heidarren statement is true about flashing  C1200 router (EU firmware) to US firmware. Need to first flash to the firmware as listed in Edit 7 of your first page. After flashing to the beta version you'll be able to then flash to US firmware.
Yes i do find the 5G signal much stronger after flashing to US firmware. Surprisingly the 5G signal is even stronger than 2.4G signal behind one wall at 10 feet away from the router.

US firmware do have the capability for WDS. I'm using mine with 5G as backhaul and also 5G as SSID wifi. Just follow @JohnLai advice in page 29.

For the power supply, i tried both the stock power supply and one with 12V/2A output. I find that the wifi signal output is the same strength. Stability not sure yet but I'm testing the router flashed with US firmware using stock power supply. Will see how long it remains before it reboots?

Aspick , heidarren and eugenecctan = Any random reboot issue encountered after flashing USv1 firmware? Remember to report back.

Second question........did you guy try to flash USv2 or USv3 firmware to the EUv1 hardware? From previous posts made by you three, it appears flashing USv1 firmware to EUv1 hardware work perfectly. But, how about USv2 and USv3? 

Guys, I have setup wireless bridge with my old tm Tplink ac1200 (flash to US firmware for faster 5hz) with the new tm d link ac1200. I am thinking to upgrade d link WiFi router because it seems not stable. The main issue now is I forgot my Tplink password and username. If I were to set my new router to the same name as my current d link router. Will the Tplink wireless bridge able to connect to new router automatically? Thanks sifu

Any comment? Thanks.

Most likely will not work. The SSID and MAC Address are used for bridge. So, using another router will have different MAC.
Why not hard reset the TP link AC1200?

Can show how and where you place the foil?

The antenna coverage is 360 degree. By doing this, you boost all the signal to the front 180 degree.
This is effective especially your router is placed at the corner of your house/condo.