Do you have an example of one that you know won't run? Effectively all the routers should be flashable unless I'm mistaken and any of them that include GPLv3 or LGPLv3 software must allow it to be custom flashable due to the anti-tivoisation clause.
FCC prohibits you from intentionally flashing custom firmware with the intent to broadcast illegally. You aren't banned from flashing and there's a very vibrant openWRT and DD-WRT community.
The last I read about it was this https://www.tp-link.com/ru/support/faq/1058/ which didn't exactly sound positive. If the safeguards are software only then custom software can break the law using it.
> As part of the Compliance Plan, TP-Link also agrees to take the steps set forth herein to support the development of software by third-parties, including open-source software, for use with its routers, which comply with the U-NII security requirements.
Essentially they were told "Limit radio parameters from being set where possible but you can't ban custom firmware" and that their immediate "oh lets just ban custom fw" response was insufficient and needed to be resolved.
Nowadays any modern router from TP-Link can be flashed to OpenWRT with the generic OpenWRT install instructions.
When I was shopping for things a while back, the impression I got from the OpenWRT forums was that a lot of it is using older versions of OpenWRT with proprietary SDKs from silicon/platform vendors and it's not really upstreamable.
