That's what I hear - from Ken and others. 13mm = about 20mm in FF which is pretty nice. I used to have the Nikon 20mm F1.8 (I think it was) when I shot with my Nikon 800e's. Now THAT was an excellent lens.
Angry photographer Ken Wheeler just did a review on it.
Says it is the very best and sharpest ever. Rates it a 10, only
complaint is the price he says which is high for Viltrox
469 I believe and Ken said 360 more like it but highly recommended it as perfect.