Consistency question - different rules at each house

My 9yo son told me his mom lets him have screen time way later than we agreed, eats less healthy food, doesn't enforce homework time. I try to keep things consistent but at some point I can't control what happens at her place. Should I even bring this up with her or just accept that he'll have different rules and move on? I don't want to be that guy but I also don't want him thinking homework doesn't matter.