...KnockLink for safety use.
While I haven't tried the KnockLink per se, I have experimented with a similar device made by another manufacturer. If one's car is fitted with an OEM knock sensor fine, but if not, it gets more complicated. Knock sensors come in two basic types, resonant and non-resonant, also known as flat response type sensors. The resonant sensors tend to be more application specific. Each motor has its own resonant frequency at which knock occurs, being dependent upon cylinder bore among upon things.
Using a resonant type knock sensor in a motor other than the application it was designed for can result in false warnings. In my personal experience testing 2 different GM resonant knock sensors in a 4 cyl turbo motor, the sensor would regularly confuse valve train mechanical noise with knock.
While it is true that the display sensistivity may be turned adjusted, without actually being able to hear detonation one runs the risk of "desensitizing" the unit excessively. Inaudible knock could be occuring without one being aware of it.
Below is an interesting primer on knock sensors and the signals they produce:
http://deviantmethods.com/bigmoose/pages/knock.htm
Here is another site with more information on flat response type sensors:
http://www.delphi.com/pdf/ppd/sensors/et_flat_knock.pdf
For a universal application I'd be inclined to go with a flat response type sensor, which is also what Bosch Motorsport recommends with their stand alone racing ECU's. However, I have yet to find an aftermaket logger that will read their low voltage output without an amplifier.
espritGT3