This costume is definitely cute.  It is very well made with good material.  Washed it before and after wearing and it is still holding up well.  It is very thick so it will keep your baby warm when trick-or-treating outdoors at night.  But if this is for an indoor party or a sunny day-time photo-shoot, be careful not to overheat the little one.

One big con is that since it is a pull over, it is hard to put on.  If your baby is fidgety, good luck.

I bought a Small (6-12 months) for my 7-month-old son (about 18 lbs) and it fits him with just a tad bit of room to spare.