As I said, I haven't played around with the JTAG or serial port.
I suspect the JTAG port is for firmware writes if bricked, monitoring RAM or other registers for debug purposes, etc. There are a number of free and/or open source JTAG utilities around, will need to figure out things like processor and flash brand and models to figure out some of what you need to send through the JTAG port to get results.
The serial port is most likely to connect a terminal or terminal application to to have access to the OBi devices console.
When I have some time I will play with it, but I might wait until I can pick up another one to play with when I have some extra cash.
Dave