You do not need reservations. We ate there for breakfast and it was not crowded at all due to everyone being in line for Gringotts. There is a person standing at the front. He asked us if we had reservations. We said, "no " and he said, " you do now!" He then let us in. At lunch the next day, we got in, but the line was quite long. It moved fast though and we didn't have to wait long for our food. We loved everything we ordered!