The quality is very nice, and this leotard seems very durable. I ordered it with the pink Bloch tights and it is a perfect match.
I ordered the P (4-6) for my daughter who wears a size 4. It fits fine, but the straps are a bit loose. I do not think it runs small.
I bought a black, size P(4-6) for my very petite 3-year-old (upon hearing the "runs small" reviews). This dress fits her a little loosely, yet has much room for growth. She LOVES the compliments she's received :)