Main dog.. yes. I haven't seen a pure -F 400 (ie non-converted BCF etc etc) without an RDDU. Have seen one with a read-out in the nose, most with read-outs at both nose and side doors, next to L/M panels. They show gross weight and % MAC; digital displays that change as the aircraft gets lighter/heavier and actual cg value during loading/offloading/fueling.
If you're talking pax a/c, all bets are off; have the grand total of zero experience with those. 20 years -F.