You have bypasses because the pump is flowing a lot of fuel and the regulators are restricting fuel flow down to about 6 lbs so you want excess fuel going back to the tank so the pump isn't straining itself to death. Whether you're idling or going 200mph, the electric pump is pumping the same rate.
I had a mallory 140 and it was useless on my 572ci Camaro. I switched it for a BG250 and that was fine. Originally it was mounted in the trunk with a BG400 I used for the nitrous but after a burnout the car cut out because of lack of fuel and gravity etc. I dropped both pumps under the car and it was all good. Spend the money now on a decent pump. Save you in the long run. You don't want an engine leaning out.