Six months ago, I bought myself a Samyang 14mm f2.8 autofocus lens (
https://www.samyanglens.com/en/product/product-view.php?seq=389) for the Z6 camera through an FTZ adapter.
I immediately upgraded this lens to a new firmware (v.2.0), all functionality works flawlessly. Manual focusing also works perfectly, focus-peaking on the camera screen is visible perfectly.
As for the image quality, it all depends on the shooting conditions and depending on which lens you want to compare this image quality with. Comparing this Samyang to the Nikon Z 14-24mm f/2.8 S at 14mm, you obviously can't get the same great results.
If we close our eyes to the difference in the maximum aperture of one stop when comparing this Samyang with the Nikon Z 14-30mm f/4.0 S, then in this case we can already talk about similar indicators of the quality of the resulting image, but one lens is better in some indicators, and the other lens is slightly better in other indicators (of course, if we are talking only about a focal length of only 14 mm).
Here's a pretty detailed review of the AF 14mm f/2.8 F lens with technical data and sample photos:
https://www.ephotozine.com/article/samyang-af-14mm-f-2-8-f-lens-review-32597
One more question remains - for this lens Adobe does not have a correction profile for Adobe LR, the official Samyang website also does not have a correction profile. I had to take care of this issue myself and make a correction profile myself using the Adobe Lens Profile Creator 1.0.4 program. If you do not want to independently make a correction profile for this lens, then in Adobe LR you can apply a correction profile to it for Sony - it also removes distortions well, but not completely, when shooting architecture, you can sometimes see curved lines where they should be straight.