My review of the metal housing with filter mount for Xiaomi Yi Action Camera. Bought on Ebay, came with Kenko 40,5mm filter, Lens Cap and mount to attach it to GoPro gear. The filter mount had to be shortened on a lathe by aproximately 1 mm due to vignetting problem in video mode. With lens rectification mode ON, there is no vignetting at all, so the shortening is not necessary.
