I have been using baby sleeping bags for a few years now as we have a large family. I think they are fantastic at keeping babies warm. I have always worried though about little arms getting cold so when it's super cold outside I have sometimes put a long sleeved vest under a babygro to keep them warm. I would also check babies neck to see if they were warm enough. I would never go back to using blankets/sheets as I've noticed our babies will always try to put things on their face if they can so I removed all blankets from the cot