The Essential wrap is a birth to potty wrap available in poppers or velcro.
It will fit from birth usually to potty training, though some babies may require a large, depending on how soon they potty train.
This wrap will work on a newborn if you are using a fitted nappy beneath it, rather than say a pad folded terry, but it will not look as cute or close fitting as a small classic wrap. The idea is that if you are trying to save money then there is no need to buy small then medium wraps, this will do the job from birth. If your baby is about to grown out of the size one range (about 15/16 lbs) then definitely go for the Essential wrap, since it would probably be a waste to buy the smalls. Hope that all makes sense ! :)