Is this a trick question? (The links point to the same cover)
I used the Nashbar bootie last winter. It is water resistent not water proof so in really wet conditions my feet would get wet. They lasted one winter season before the zipper started breaking down. They really help alot in keeping your feet warm but I'm not sure if they are of the best quality.
The Pearl Izumi shoe cover linked may have better water resistance but the lack of sole I would find a problem in winter conditions. The roads and walk are slippery enough without walkin on a slick shoe sole. I'm not sure if either will work with mtb shoes.
2002 cannondale r400, 2006 kona smoke, 2005 scott speedster s30
I tried the Pearl ones and they wouldn't fit over my cycling shoes (the guy at the store told me they would only fit over low profile road shoes and mine were MTB shoes.