Excellent product, saves time, and money! How? You don't spend money on snowsuits, sweaters, mittens or thick clothing, only to be quickly outgrown, having to be replaced. I put a hat on my son, and put him in the Bundle me, where he stays warm and sometimes even sweats.
Please bear in mind that you do need a hat.
It fits well in the Graco Snugride infant carseat, and I think it should be okay in other seats. I like it that my baby can go out in whatever he is wearing at home, so long as I put him in this. When it's warm in the car, in the store or when I reach home and I don't want to disturb his sleep, I unzip at the sides as appropriate - as little as or as much as I want.
The one problem I see is that I usually tuck the sides of the cover round the sides of my sons head. However when he is active or simply playful, he beats off the cover with his hands, and I usually have to calm him so he leaves the cover in place before I venture into the cold. If you have a very active baby you may want to bear this in mind.
It's becoming a favorite shower gift from me to friends. It makes life easy for me and the thought of going out in the winter months is less daunting.