|I had 1 M/L cover that came with my starter package. It was so close in size to my 2 Mediums, that I just used it with them. When my son was getting too big for the Mediums, I just sold my M/L right along with the Mediums to buy Larges. I didn't see much difference between the Mediums and Med/Larges and don't think it would be worth the money to intentionally buy them. But I have a hunk of chunk, so he grew fast out of everything anyway. Maybe if your child grows "average", they would fit long enough to be worth it.