Yep. I could often work out in seconds what would take ages to sort out with oscilloscopes etc. I know what you mean about baud rates too - you could at least get a basic idea if it was right.

It also had a snoop function (TX, RX or both if half duplex), null modem, RS232D (RJ45) all in one as well as the pass through. About the only thing it couldn't do was RS232D to RS232D but simply two of them joined did the trick then.

Otherwise called a "Christmas tree"...