It’s the same thing. Either repeal legal tender laws and watch a zillion banks open with gold/silver backed paper notes. Or, designate gold/silver as legal tender, and watch a zillion banks provide paper notes backed by said PMs.
There is a difference. With legal tender laws the government can and will regulate the specie content values of the coins (coin clipping), and will regulate the exchange rate between gold and silver (price fixing). Without legal tender any attempt at funny business by the government will result in a switch to private or foreign coins.