You're first sentence in reply to Floobydust was correct, you don't know what you're going to get. As determined well into the T12 CFW firmware thread (and as large as it is, I don't blame you for not wading through it) Flooby and I discussed this and came to the conclusion that version numbers don't mean much. There are so many changes that KSGER makes to the HW that its useless to use their version numbers to determine anything useful (when I bought mine, it seemed to me that "3.1s" meant it came with the black PCB, but I think it was Floobydust who showed me that there were some "3.1s"'s that used green PCB). Not to say that the HW is the same between them, but the only useful measure that determines one version from the other is that V2.1s does not have a Russian language option while V3.1s does, at least that was the difference that KSGER touted on their Aliexpress store when I bought mine (which was about 2 years ago, so it may have changed and now both versions have Russian menus). I opted for the 3.1s, I just could not resist getting the "latest".
If you plan to use DavidAlfa's custom firmware on yours, it may have been better to get the Quicko. If I recall, I think it was more straightforward to mod it for use with a JBC 245 soldering iron and his firmware was pretty much made for it, since that was the model he bought. But it has been successfully used by folks with KSGER's of either versions. In the interest of full disclosure, I don't use David's firmware, I use the stock OEM firmware that came with it. I find it works well and since the general consensus is that clone JBC tips are not as good as the clone T12 tips, I do not feel a need to attempt to install it because I don't do enough soldering to need to upgrade to genuine JBC tips, the T12's work well enough for what I do. I do like the idea of having a choice, though, should JBC tip clones get better.