Had one on my Duster's original 340 and hated it...car never ran right no matter the tuning we did. Bolted on a 650 Holley and it was like night and day, throttle response was better and the car picked up 4 tenths with the (untuned) Holley. Never looked back.
As mentioned, for a mild street driver they can be decent. Had a 360 with one on it and it ran fine. I think there are better choices out there though.