One of my employers once ordered a pallet of Huawei routers. They turned up with a custom firmware provided by a different ISP. It was completely locked down, and only configurable via TR-069 and some proprietary Huawei ONT magic.
I also had a customer once that deployed a series of routers that were cloud managed only via the ISP. Not even TR-069 but they just did DHCP and phoned home via a proprietary protocol. Magic my customer said, he can just reboot customer routers remotely. The company that manufactured that router went bust 8 months later, leaving a bunch of preconfigured routers without a cloud portal and no path forward. Surprised I havent seen a DNS hijack published for them yet.
the thing went in the bin the next day
All major ISPs in the US do not do this, e.g., AT&T, Verizon, Comcast, Frontier, etc. You might be right for some ISPs that are nicer, but this advice is completely ineffective for most US consumers.
Quite a long support time.
To me they seem to be the best standard solution that can also be setup by a "beginner" user.
I turned off remote access and TR-069 through a toggle in the settings, then changed the admin password. Really, that's all you need to do to take control of one of these routers.
There are good reasons to dislike the AVM routers, but their software is actually pretty solid in terms of customisation and network security. It's not a bad device, and the large scales ISPs can order them at they can be had for a significant discount as a rental compared to buying your own in a store.