Is there something, specifically, that you're concerned about?
Breastmilk and cow's milk taste about as similar as coffee and Pepsi. So baby won't be looking for cow's milk thinking it's yours.
Nutrition-wise, as long as baby is getting all of the nutrition he needs and can physically chew (if necessary) and swallow, he can eat/drink just about anything. Things like milk are actually a good way to get baby extra calories if he's behind on his growth curve, because it's pretty calorie and nutrient dense, without being hugely filling. This can be something to watch out for, but it's on par with any other foods and keeping everything in moderation, while watching your child's cues.
The main thing that you might have to watch out for is lactose intolerance. However, if you've been consuming dairy products while pregnant and/or breastfeeding and it hasn't caused problems, it's not likely to cause problems with him consuming it directly.