Since I run MyDMDX quite litereally by placing that laptop on the same rack that has the DMX Operator and the OptoBranch/4, if I have a fail-over, I simply swap the cable from the OptoBranch/4 input. I have a cable wired to the DMX Operator and a sepparate cable(loose) to the MyDMX dongle. My switch-over takes seconds. The argument for a fail-over solution is entirely valid and it is a justifiable concern for those using computer/PC-based solutions, as opposed to dedicated hardware.
I figured the pairs of outputs would be in parallel. The unit is advertised and in the manual states it is a 4-way split system. The fact that it CAN drive that many outputs is just something a few people have taken advantage of. For me, it's almost an ideal unit. I can send a run back behind me, a run to the stage, and then another 2 runs often side to side for follow spots and keep it clean.
I'd ideally like another one at the stage. Floor/footlights run, front truss, rear truss. Anything off the sides can hang off the front or rear truss runs, leaving me an open split in case anything crops up.