Out of curiosity, I ran the same swap ($1000) each on MetaMask and a DEX aggregator. MetaMask's "best price" already has their 0.875% service fee baked in before it even starts comparing routes..

Ultimately, MetaMask swap paid 981.74 USDC (-1.825%) while DEX aggregator paid 998.4 USDC (-0.16%).

The difference isn't that high on this test but on higher amount it could be really annoying, do not use MetaMask to swap, especially when their wallet sucks.