I bought my jamma harness from Bob Roberts, also bought one from ultimarc. I dunno who Andy gets those from but it just seemed very cheap. Not only that, but it wasn't keyed and there was no labels for it. On the plus side though it came with the quick disconnects already on the wires. No instructions at all though, and since I have never done this before I was confused by a couple of the connectors.
The one Bob sends comes keyed and labelled. All the wires are different and it's extremely easy to tell which is which. It also seems much more sturdy. I liked being able to add the quick disconnects and whatnot to it. Both were about the same price.