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I've seen these before and thought it would be handy. It's been fun just to see what it shows on known components and it does have some limitations. It will not accurately detect higher power thyristors that are known to be good. It says "unknown or defective component". It will not provide reliable performance for MOSFETs that have have high VGS thresholds, and it has trouble with Darlington transistors with built-in base-emitter shunt resistors. It will not accurately detect JFETs with low Idss (eg. PN4117A) The test current is up to 6.3mA or so and it can put up to 5V reverse voltage on a component while it's trying to figure it out. That said, there are some things it could damage. The MPSA06 is an example with it's BVbeo of 4V or the 2SC2705 with it's Ib absolute maximum of 5mA. When it measures diodes, the forward voltage drop is at 6.3mA or so. It also measures the capacitance of the diode. It seems to almost always measure PNP transistor gain at around 6mA and NPN varies. It also measures the Vbe at that current before displaying the pin-out. Testing capacitors, it keeps testing for a while so you can adjust a variable/trimmer type and determine range. It will not tell you if the leakage current is unacceptable for a timing or control loop where that may be critical. Resistance seems reasonably accurate. Be aware of the 6mA test current. A 5Meg trimmer may not survive that close to it's minimum resistance, for example.
All limitations aside, it's a nifty device and well worth the price, especially for just the inductance function alone. The measurements are reasonably accurate and it's a great device to have around to help identify unmarked components. Despite its limitations specified above, buy it...
