First, thank you all. I have now a much better picture. There seems to be consensus about MT7621 being reliable. Good to know. Again, thank you all.
I have to build a 22.03 image to see how the requirements have changed, now that dropping IPv6 isn't a viable option anymore. We were used to put Luci and IPv6 out as a matter of routine. For the time being, it looks as if I could fit it into an 8MB image, but I still need to strip out some more things, then look how the utilities we want fit into that image, then look at RAM consumption. But I'm pretty confident it could be made to fit into a 16 MB image without much hassle, and that 128 RAM will be enough for our need for some years to come. Yet this has to be proven. I hope to do it before next week.
We have no problems with difficult installations as long as they are possible and the result is reliable after that. So, reading a flash chip, etc, could be done, no problem.
After a meeting with the friends, it has been decided to purchase some ram and flash chips to try and upgrade some of our old ath9k devices, and to purchase a router to test it. I'm the one making the decision about which one.
Since it looks as if a 16/128 device could be good enough, I'm leaning towards cheap ones that are about €30. That would mean Xiaomi Mir4A, Cudy WR1300 and ZBT WE826. First two could be obtained from local vendors that can be contacted by phone to make sure what version we are about to get. We had some nasty surprises in the past when the device was delivered an realized hardware had changed without notice. Fortunately these were small purchases.
So, any additional information about of Xiaomi Mir4A and Cudy WR1300 would be greatly appreciated. Any information, not just about reliability.
@reinerotto Hi, nice to be again in contact with you. We find ZBT WE826 quite interesting, mainly because it looks as if you have quite a few of them deployed. But there are some different models. We would like to have 802.11 ac since that could be obtained from the other two candidates, and upgrading the hardware in that way without getting ac wouldn't be easy to explain to our people. We found an Alibaba provider but the model would be WE826T, without ac and with LTE hardware which we are not interested in.The price, after transport, VAT and taxes would also be higher. Could you give us some more info about it?