I have never owned a logic probe, but have sometimes thought that they would be a valuable tool, and someday I may buy one:
When you are actually building complex logic, (and even more so, when repairing complex logic), you may find yourself needing a logic analyzer. These things are tricky to use, but absolutely invaluable. The standby used to be the HP xxx, which was a big expensive machine the size of one of the old oscilloscopes you roll around on a cart. I have just discovered that these days there are inexpensive logic analyzers that you plug in via USB and run via software.There is an 8-channel unit by Saleae Logic for $150 (and a 16 channel big brother for $300). Adafruit sells these, and they would be an amazing bargain, except there is a much more amazing bargain to be had. The units are called the "logic" and the "logic 16". The software does run on Linux (32 or 64 bit), but does not seem to be open source. You can download the manual without restriction.
The amazing gadget is the "Open Workbench Logic Sniffer". It gives you 16 channels for $50 and people like it (and those who bought the Saleae device kick themselves). Mind you, there is nothing wrong with the Saleae device other than the extra $250. It is designed to work with the "SUMP" open source logic analyzer client. The main complaint is that the $50 price just gets you the circuit board (ready to go), and you have to add an enclosure and buy probes separately.
The next item down the list is the Logic Shrimp. This sells for $35 and has more channels. Some people say it can be useful when you need a longer capture.
Last is the Bus Pirate, which is not really a logic analyzer, but gets used as one for some applications. Two channels.
Tom's Computer Info / tom@mmto.org