I have them...live in the desert so they've not seen much use. They did help once on a cold, rainy road tour. They kept my feet warm, although not really dry. To be effective they don't really breathe well, so your feet end up damp from sweat vs outside moisture. Probably worth a shot if you're in a colder climate.
Have used them all winter with summer MTB shoes in PA for a few years. Worn them in snow and single digit rides with warm feet. While they are warm and waterproof, as mentioned your feet will be drenched with sweat. I used them as an alternative to booties which I loathe.
This year finally bought some winter MTB shoes. We'll see how they work, for really cold might wear them with winter boots.
I wore them for the first time the other day because my shoes were still wet. I had to wade through a stream and they kept the water out but me feet we're still wet when I got home. They were quite bulky as well.