Protein for breakfast?

I was recently told by a co-worker that having a muscle milk in the morning for breakfast is not good for you. I was wondering if this was true. I have been using them as more of a meal replacement because they are low in sugar and high in protein. Am I only supposed to use them after a workout? I thought that a high protein diet was great for weight loss. I just would like someone to enlighten me a bit. I work 8-10 hour days at Walgreens and even though they are on the corner of happy and healthy there food product choices are anything but. So when I forget to eat breakfast at home because I'm rushing out the door I buy one about 11am or so. It takes my hunger away and helps me make it to lunch. Thank you in advance.