I have installed Asuswrt-Merlin on a new RT-AC66U. The device came with 126.96.36.199.140, which I see from the Asus site was the very first version. In the Asuswrt-Merlin README, the Installation instructions indicate "Simply flash it like any regular update. You should not need to reset to factory defaults, unless coming from a version that used a different nvram size." I'm not up on the history of "nvram sizes" of different versions. I did flash the latest Asuswrt-Merlin (188.8.131.52.246.20) using the "Upgrade Firmware" function in the web gui. It seems ok ... but before I go further configuring things I'd like to make sure I haven't missed any key steps (due to the "... unless coming from a version that used a different nvram size" warning). The only oddity I noticed so far is that after poking around with the device last night, I powered it off... then when I powered it on tonight, nothing could connect wirelessly to it. I power cycled again and it came up just fine. Thanks in advance!