I already flashed OpenWrt snapshot on the EdgeRouter 6P. As far as I can tell, it appears to run smoothly as a client in my network. I did not yet flash OpenWrt 21.02.1 on the DGS-1210-28, but plan to do so in the near future.
I don't think you should sell your ER6P. What might be more interesting is to build your own images from master since master is (or can be) always in flux. There's times where it breaks, and there's times where it's stable for months. Right now the iptables nftables migration is in full swing e.g., in master, and I believe developers are gearing up for a new release branch (push to the new 5.10 LTS kernel hints at that, amongst others).
What I tend to do is (when it's technically feasible) backport support for the device in question to the latest stable release and build an image off that. From what I can tell, the patch adding support is rather trivial all in all. So that looks like it could be easily backported to 21.02 (although the changes of it being accepted are slim). I could take a stab at it and provide you with a patch, if you'd like. Then you'll just need to build your own image off 21.02.
You're aware OpenWrt does not support the passive PoE capabilities on the ER6P?
Marvell bought Cavium so they own the IP now but Cavium hardly bothered with upstreaming support, and it looks like Marvell isn't really doing that either so far. Make of that what you'd like. I personally sold my ER4.
While I am curious about building my own image (never done that before, should have all necessary resources available, though) and greatly appreciate your offer of providing a corresponding patch, I am at a loss about how to judge the memory leak issue. My knowledge and skill don't suffice to truly grasp the meaning of it, despite the links you shared.
That being the case, it seems like a risky thing for me to rely on a main router that has a bug hidden away somewhere, of which I am illiterate... Or am I being too afraid of what I do not understand? You eventually selling your EdgeRouter adds to this gut feeling. I think I shall study some of the hardware recommendation threads and evaluate alternative routers. Which one did you replace your ER4 with?
I picked up a MikroTik RB5009UG+S+IN myself but until now it really has not been a walk in the park, trying to get OpenWrt onto it. The SoC inside it is well supported though (Marvell ARM) so once the kinks get ironed out it should get better/easier. But getting OpenWrt on the Ubiquitis is a piece of cake, compared to it.
The memleak might get solved, but I am not skilled enough to look into it and the people who are can't narrow it down at the moment. The hardware support upstream (in the Linux kernel) is not what you'd want it to be for a device you'd expect to use for a few years. To illustrate: some of the Octeon code got removed for 5.9 I believe, only to be added back a bit later. That's telling. That's not something kernel maintainers do on a whim.
The hardware recommendations subforum is a good thread to start, and this post might get you on your way a bit:
OK - thanks! I shall definitely not follow your example regarding the MikroTik
Instead, I will study the recommendations a bit more closely and see what turns up. Since I do intend to keep using whichever router I end up configuring for as many years as feasible, your feedback makes the ER6P seem imperfect.
Just to follow up and not leave a loose end: I have decided to try setting up a Raspberry Pi 4 as main router. I will hang on to the ER6P for a while longer though; in case things don't work out for me with the RPi... Thanks again for sharing your information!
This thread has contributed greatly to my decision making: