brendanwrote a review of Castelli Diluvio Shoe Covers 16 on December 15, 2012
Familiarity: I've put it through the wringer
a bit of a battle to get over the velcro elements of your shoe, but ultimately they keep your feet quite warm. with just one pair of wool socks and these on, my feet are not at all cold in temperatures as low as the 30s. will update review once weather permits me to try them at lower temperatures.
the material is simply neoprane, nothing fancy. it blocks wind and soaks up water but still insulates. when i remove them after a ride, they are usually moist with sweat but with no detriment to my warmth.
best features: zip up rear, reinforced ankle (superior to diluvio non-16 which lacks any reinforcement there and is likely to split up the backside the first time you pull it on), large reflective strip going up entire back of boot, warmth & windblocking, blocks middle vent on sole of shoe between cleat and heel pads
cons: on-off is a little violent due to the lack of any sort of smooth inside surface (it's just one noeprane membrane). i sometimes think it won't last more than a season. but only time will tell
sizing: castelli's size recommendations worked (size 43 real shoe, order L/XL and it's very right)
overall: buy if you want to stop shopping around for winter covers and just be warm