I'd check again, I've been told that one doesn't have the drive to run the RS Commander. I don't have any here, and since I heard that, I don't bother to buy them and run into that problem! I use the second one in the list, last time I installed it, it had no problem with the serial data. It's cheaper than the MC-EX as well. ;-)
One difference is the RCDR doesn't have incandescent light outputs, it has an LED output for the lights. That doesn't bother me as that's all I use.
Here's the wiring diagram for the RCDR.