TP-Link TL-WDR4300-V1.3 (OpenWRT - AR9344 - UniFi)
I flashed this device from stock firmware to OpenWRT using the Attitude Adjustment 12.09 RC1 built, confirmed the switch & vlans setting can work on UniFi ! 
References:
- OpenWRT : http://wiki.openwrt.org/toh/tp-link/tl-wdr4300
- Attitude Adjustment 12.09 -rc1 : http://downloads.openwrt.org/attitude_adjustment/12.09-rc1/ar71xx/generic/
- Stock firmware : http://www.tp-link.com/en/support/download/?model=TL-WDR4300&version=V1#tbl_j
FailSafe : Yes, once the Sys light appear, press the WPS button at the back, then able to telnet via 192.168.1.1
Back to stock firmware: Yes, just flash with the stock firmware without the word "xxxbootxxx"
Flash from stock firmware to OpenWRT process
Always perform Factory Restore before & after flashing 
Default IP is : 192.168.0.1 User=admin Password=admin


Once Factory Restored, go to the following and flash it

DO NOT touch anything until it's completed !!


Once flashed to OpenWRT, default IP : 192.168.1.1
Straight Login & Perform Reset


Once done, you may setup as usual ! 
Can refer HERE for some setup idea.
For Switch & Vlans setup for UniFi, see below
This is the original Switch layout

Setup as follows for UniFi

System connected to UniFi, both internet (vlan.500) & IPTV (vlan.600) without any problem 
However, the WiFi seem unable to turn-on simultaneously, could be bug in this built ..
..


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