This first-ever-installed sundownloader was made of glass-reinforced plastic; rough, shape not ideal. It is mounted on a balcony rail above a West-facing terrace in London, England (latitude ~52oN, longitude ~0o) and these photographs were taken within 2 minutes beginning at 3.47 pm on 3rd December 2016. Though tricky to explain they do show principles and advantages clearly. The mirror is convex, NOT concave; width and height vary with compass direction.
1] South is to the right and North to the left: the observer is standing South-West of the mirror looking up at it and a bright patch shows that some light is reflected and/or scattered towards him, whereas the left-hand area of the mirror appears dark gray because sunlight striking there is not re-directed into the camera's eye.
2] This was taken from underneath the mirror and shows high-intensity light (too bright for the camera) coming straight down from the bit of mirror that was dark gray in the first picture!
3] A few seconds later the sun drops below buildings to the West.
Conclusions: Light of midsummer, mid-day intensity is available at midwinter sunset. The sundownloader sends it downwards including straight down, but instead of being focused light is spread over a moderate area so there is no risk of scorching.