There's no way to know from a listing or listing photos.
Even when photos show the v1 model, it's still possible the seller just didn't update the photos and/or are just using generic stock KZ photos.
The ONLY way to know 100% is to ask an individual seller to open it up and physically inspect the IEM. You need to pop off 1 of the silicone tips, and if you see a brass/gold ring with NO mesh screen in the nozzle, you have the v1 model. If it's a stainless steel mesh screen, it's the ZS1 v2 (which is junk in comparison).
We're currently experiencing a similar issue with the ZS5 v1 vs v2. The ONLY way to reliably tell is to shine a light through the mesh and look for 1 vs 2 BA drivers. And everyone is looking for the ZS5 v1, which is like searching for gold.
Here's a photo of the difference in the ZS1. It's the same photo I sent to 50 or so Aliexpress sellers, until I got ONE to reply and verify if they indeed had the correct brass ring version. Others may have had it, but either there was some sort of language barrier problem with what I was asking (ie non-English sellers) or some sellers were just too lazy to physically check the IEM and didn't care. The photo shown below (which I sent to sellers) had simplified language, to try and eliminate confusion (using words like golden instead of brass, etc).
I'm sure there are a quite a number of ZS1 v1s still out there on a few seller's shelves. But you'd probably have an easier time finding the lost city of El Dorado or Atlantis haha
If you do go looking, I would recommend trying the smaller more obscure sellers on Aliexpress and also ebay. Any larger seller would have moved more inventory and would have received the v2 upon KZ reorders. But if you had a little mom and pop Chinese shop that is ultra low volume, they might still have 1 still sitting in inventory out of the original 5 they originally ordered.
Heck, it's possible that the Fasttech link you found are the v1 model.
They are worth the time spent searching though. It's like a basshead's dream IEM.
I got lucky and found a seller with 1 - perhaps you will too. It doesn't hurt anything to send out the messages and ask (I just copied and pasted the same message over and over).
I wish KZ would make another batch of the original ZS1 v1 - call it ZS Special Edition or something. They used the same shell ZN1, ZN1 Mini, and the ZS2 (the ZS2 also sucked in comparison). But the ZS1 v1 had a crossover and a brass bass ring in the nozzle. So even if you got a ZS1 v2 or ZS2, removed the stainless mesh screen and somehow rigged up an identical brass ring, you'd still be missing the crossover.