As I see it, you fear cheap chinese stuff won't last for even five years, even for non-intensive use, based on I don't know what kind of data, probably just western China haters hearsay. Also, you are not willing to spend the bigger amount of money needed to buy the better, overkill for your needs, western stuff available, neither used nor new.
Well, I really hope you don't behave the same way when it's time to put a preservative in place. Just saying.
Sorry to be blunt, but you are wasting both your time and ours looking for the holy grail. What you are looking for doesn't exist, period. You are not going to get a new JBC/Metcal, etc, at the price of a Quicko/Ksger
All the possible, well-known, viable options have been already given to you, yet you continue to putting yourself into that self-made conundrum.
The way to solve that conundrum would be to read that 169 pages long thread about custom firmware. It started in March, 14, 2018, so more than 6 years ago. That's more than the five years you would want your prospective Ksger/Quicko to last. Then you would have a good idea about how long these stations last. That wouldn't be hearsay but fact-based user reports. Quick answer: very few people reported his cheap chinese soldering station ceased to work, particularly if they got a top-chinese-tier one. Like that Quicko 958. Of course chinese quality control isn't that good and you could have bad luck. But probability is really on your side, and what you do expect for 50 €? I know, you want your cheap station to be like a 600 € one. It wont happen, man.
Of course reading 169 pages would be a big waste of time when you have been already given the answers, not just about chinese cheap stuff, but also about expensive, better quality western stuff. You would be wasting only your own time, however, and that wouldn't be a so bad thing.
I have to say, worrying about if it could last more than five years, while saying you aren't going to use it intensively, is ludicrous, do you realize that? Thinking about getting a new JBC one, for that kind of work, while thinking it should cost about the same, is even more ludicrous.
Man, no matter if you choose the cheap or the expensive one, put that preservative in place and have fun.
Edit: typos