act of god. For the sake of a few dollars and some fittings, it's unsafe and stupid not to put one in.
Have any of these guys tested the brakes for rear lock up under various conditions? Having your rears lock first is not fun when you really need to stop and or avoid obstacles. By the same token - if not enough pressure goes back there, the rears aren't doing their full job, which is to help the fronts decelerate the car at the highest possible rate. A balanced braking system is awesome and makes any car safer.