Just realized that the maker fee rate for the USD1 contract trading pairs on bn is 0. This is more suitable for large orders—makers save quite a bit after filling. Plus, a while back, the trading depth for large USD1 orders was much better than USDC. USDC at various price levels is mostly dominated by small orders. The only issue now is that there are too few contract trading pairs supporting USD1. Currently, it's just BTC/USD1 and the newly added ETH/USD1. Now that the depth is sufficient, it would be even better if the number of supported trading pairs could increase.