Yes

Latest stock firmware is fully compatible

Tested and confirmed

You buy V1 or V2

If in this case, flash to OpenWRT.

I was using Black Widow since Wed and i noticed that sometimes my connection freezes and have to manually off > on to resume my connection and the Purple does turns to solid blue and Hanged.

Now i am using back AA and so far so good. So those of you that is using AA, try BW BB at your own risk. 

Btw, i have 2 # Mr3420 one on AA and one on BW BB.

This is my AA

[attachmentid=3389610]

am still using the above AA version for my mr3040V1 ,. so far is the most stable and best in consistency openwrt,..



reason to support my statement above is my load normally always between 0.21~0.25 only,..

which when i use blackwidow or huntsman, my loads is between 0.79~0.98 
router load when running torrent 0.21~0.25
[attachmentid=3407212]
router load when not running torrent 0.3~0.10
[attachmentid=3407218]
and when the router load running too high, sometimes the webinterface 192.168.1.1 become unresponsive and the wireless connection get affected like request time out too,.. 

so before anyone of you think is the temperature issue for the wireless connection, this is how i setup my MR3040 V1 + Huawei E1820 ( with usb mini usb table fan blowing )
so it is not the temperature issue

[attachmentid=3407220]

my V2 stock firmware so far connected for 6 days +,..

last connection DC when around 12days,.. forget to screenshot,.

so stock firmware still the best for those who prefer user friendly and no need any fancy add on

picture tells thousand word

you should try to  set 40MHz channel width and try different wireless channel 1~ 11 to see whether the issue still happen,.. i assume  u are using 20MHz on wireless channel width and wireless channel setting on auto right ?