Greg nailed it! Good performance with good drivability and mileage.
I have had a couple Pontiac tri-powers as daily drivers. Tiny center carb has great response and gets good mileage. Step into it harder and you open up the larger outside cabs and away we go.
Notice that most of the mainstream dual quad setups on factory cars in the mid 50's were replaced with tri-power setups by the late 50's and used into the late 60's/early 70's.