So, Viltrox announced two ultra-wide primes in the Air series, with the 9mm f/2.8 being out now for APS-C (13.5mm equivalent) and the 14mm f/4 for full frame coming next month to Z mount. Both have reviewed very well.
I picked up the 9mm f/2.8 for my APS-C kit, and the long and short of it is that this lens has no business being this good for this price at this size.
It's not a perfect lens by any means, but it is rather sharp from f/2.8, and corners get very good (though not perfect) stopped down a bit. The lens is sharper than my 14-30mm f/4S at 14mm. Relatively good distortion control, though a little wavy, and the profile in Lightroom does not correct it, but in the vast majority of situations it isn't an issue, and a +6 in LR takes care of most of it, with just a hit at the edges for the mustache remnant.
Color and contrast are excellent, AF works very well.
Some samples on my Z50 II:
One big benefit to the lens is that it can focus VERY closely - about 2 inches from the front element...so dramatic close ups can be done too:
Flare control is....variable. In some cases (first image below) it shows almost no ghosting or loss of contrast. In other positions (2nd image below), there is a fair bit of ghosting, but it adds a little character and I don't think ruins the image. With the sun near the center of the frame, though, it's Holy Flare Explosion, Batman! So, just be cognizant of positioning when shooting into the sun. Overall, though, a very impressive lens for under $200 and being so compact.
Looks very good. No idea how Viltrox made such a great lenses for such a low price. I waiting for my 14mm/f4 to arrive. From what i've seen(reviews) it also looks stellar.