i seen a 8 psi rise from both pumps on at same time vs one. They make adjustable regulators for control of fuel pressure, you have to set your pressure anyways its no more effort to run them together then as you would one with a hobbs.
wiring can fail but if you wire them together and do it correctly if you lose a pump you just shut down. Let the motor open then replace then fuse and limp it home. Having one on hobbs you are relying on a switch that can fail and you have no idea it failed till you go into boost and your motor is done for.
using them together its much easier to dial the AFR in. Youre not working the pumps anymore then you would with one pump. Some like to think you heat up the fuel more by cycling more using two pumps but when you are in need of two pumps you also increase size of fuel carring lines, so the heat created by resistence from running them together isnt no where near as bad since youre lines are increase allowing more volume