It's fine as general nutrition, but isn't in any way optimized as workout nutrition. The protein content is principally (about 80%) casein, which is slow-absorbing. The form of provided carbohydrates is lactose, which again really isn't optimized for workout nutrition, being (by the time it's absorbed) only 50% glucose and the other 50% galactose, which isn't directly utilizable by muscle but must first be converted by the liver.)
The second isn't a big issue, just not optimized, and it's better than sucrose anyway. The first however could make a noticeable difference version a whey or even moreso a hydrolysate.
If however your situation is that you're in a position to make fast gains without particular optimization, then that can happen regardless and the milk may be fine.
However if anything it would be more effective to have loaded up hours before the workout rather than relying on delivery at time of workout, due to the slow absorption of casein.