This is a comfortable and easy-to-wear costume, something that can be put on quickly. The robe itself is one-size-fits-all, so a little bit gapey around the collar. I pinned mine in place to give it that distinctive-McGonagall-style neckline.
The hat (and it's feathers) are synthetic. The brim is large but the head-hole is small. It couldn't really stay on by itself. Next time I wear it I might incorporate some sort of comb or clip to keep it in place, but there isn't much fabric to work with to make this happen.
I would recommend pairing the outfit with a pair of spectacles and a wand, however even without the glasses, people immediately recognised the costume.
Also, keep in mind the robe is synthetic too. Probably easier to wear in the evenings, but was quite warm/sticky during the Queensland daytime! I wore a skirt, singlet and boots underneath.