Life saver! It helped my son transition from swaddle. I love that it is so fluffy yet so lightweight. The first few nights were an adjustment for my son but after that it was good naps and good night sleep. I didn't get to experience 6-7 hrs of sleep like other people but my son has never been a lot by sleeper. Wakes up to feed every 3-4 hrs and is 5 months old. He weights 15.5 lbs and the Small was good for him. One thing to consider is it gets warm. My son Has always been hot, and when its slightly warm outside I take off all his clothes and he sleeps just in the suit. On colder days I put on a full body onsie and hes dine.