A great idea, nicely executed. Compact and conveniently shaped, the isolator sits in a computer USB port, and provides a socket of its own to connect whatever probe or tool you want to use. It's nice to know that the unit is totally isolated though, allowing me to easily work on circuits that have different power supplies, without fear of shorting either the logic probe or the laptop due to mismatched grounding.
(Giving a "netural" rating for documentation as there isn't any provided, but frankly the isolator does one tiny simple job and doesn't really need any documentation)
First I have to say this board is really worth the money. Super small pre-programmed Arduino compatible Attiny85 with micro USB and shipping - all this under $4. However the documentation is a bit sparse, and getting this to work with OS X included some serious head scratching. This blog post pointed me to right direction.
This unit does luckily have enough power to switch on a relay (200mA max.) and not only a TTL output. The cut-off voltage is precisely 10,5V (not adjustable) The cut-inn voltage is also precisley 12V (not adjustable) There is a trick off course to adjust the cut-off voltage and that is by using a resistor in series with the input (100ohms) gets the cut-off voltage up to 11,2V. Or a voltage divider with two resistors is also possible, you will have to experiment to get your desired value.