We have BOA and USAA, S2 has USAA. We can transfer to each other, but we’re not listed on his accounts. Since he’s an expat living overseas, this is a good way to be able get him instant funds in an emergency.
I’m still on both sons’ UGMA accounts. Haven’t gotten around to getting signature guarantee/medallion stuff, since I’m not sure how to get that! The sums aren’t large; it’s a nominal amount for S1, but it’s launching $ for S2.
Both closed their kid accounts when they went to college, and cancelled the free college accounts after they graduated.