I bought these as "second" covers so I could have one pair for my road shoes, and one for mountain/gravel. I've always found booties annoying to put on and get the cleat lined up properly, so this way, I only have to remove the booties far enough to get my foot in and out of the shoe.
These booties are quite warm, and offer enough insulation to get me down to around 35 degrees, 20 degrees with the addition of wool socks and some chemical foot warmers placed between my shoe and the bootie. The medium works well with my size 40 cycling shoes, but is still a bit of a struggle to get on and off all the way.
I did take away one star because the placement of the cleat opening is simply too far forward on my shoe. The heel-side of my LOOK cleat doesn't quite clear the fabric of the bootie, so it takes some extra finagling to get it fit so my cleat doesn't randomly pop out of my pedal. Meanwhile, there is about 1.5" of clearance on the toe-side of the cleat. I don't have an extreme cleat position, so I'm certain I'm not the only rider who has this problem. Maybe something for the design team to take a look at in the future?