I pretty much live and breathe Do-It so I can't answer to the other maker's contraptions, but the Do-It Twin Injector's block rod is certainly not a handle. Note the thumb screw on the injector body bracket? The rod helps keep things in time, helps prevent any twist while injecting and the screw can be tightened so moving from mold to mold keeps things in one nice package. If you're using this as a handle you've got darned small hands.
When I am injecting 1mold I have the rod removed. I can hold the block body at the mold with one hand and pump with the other. I've done as many as four identical molds clamped together without the rod and no hassles whatever.