I fitted the Shoebox monitor and found it to be a very useful tool as it monitors the system in real time, while the motor is running, even while driving, and is very helpful for diagnosing faults in "real time".
It is basically a multimeter that checks all the systems as per the Bentley manual, quickly and conveniently, plus it has LEDs for checking the starter relay and the hall sender - it flashes with each spark of the ignition at idle, blurring into a continuous stream of light when you rev the engine.
Downside is that it is difficult to concentrate on driving whilst monitoring the digital readouts, as you need to switch channels to test different circuits. Much better to get someone else to drive while you are fiddling with it. Alternatively, pull over and check the readouts on the side of the road.
Very useful for checking the starter relay and hall sender - if the LEDS don't light up, you know where the problem is. The unit also checks the throttle control switch and all of the sender units, so you can tell if one needs replacing.
This is particularly useful for the costly O2 sensor, which requires replacing every 100,000k, and can play up in between times. The unit will also expose the shortcomings of the inferior O2 sensors that are often foisted upon us.
It takes an hour or so of precision soldering to connect the wires to the circuit board in the ECU. I had to buy a fine-tipped soldering iron, a pair of tweezers and a magnifier. The instructions are clear and easily understood.
I found the wiring loom a bit short (US Vanagons apparently have the ECU fitted in a different position) so I ran the wiring under the floormats and fitted the monitor permanently, in a console between the front seats.
Alternatively you could just plug the unit in to the ECU when required, and sit the unit on the passenger's seat.
Although it is fairly expensive it will soon pay for itself by saving you the cost of replacing perfectly good sensors in the "scatter gun" approach to solving EFI problems.
Overall, it is a very useful bit of kit which gives me a sense of security that I can solve my own problems when travelling in remote areas.
All of this will soon be obsolete if GoWesty's new EFI system proves to be as good as promised!