easy stuff is easy to do, more difficult stuff still possible. For those looking for a case, consider some simple brass or plastic standoffs to keep the board off the desk. Works for me.

Might be wrong to complain at this price, but here goes anyway.
1) one button interface works great for easy stuff, but frustrating for signal generator, PWM, etc
2) signal generator only @ 5V
3) period for PWM locked, and only @ 5V

in short, very difficult to have more than one variable for complex functions with one button interface.

There are public domain PDF files documenting the 328, where I learned that pin 1 is ground when using signal generator. Good to know

This is a handy little unit it has worked on every transistor I have tested except darlington it will tell you if it's NPN or PNP or if they are bad but not that they are darlington .but thats ok I got it for Jfets and Mosfets that it do's very well it gives all the info a hobby builder can use and thats all I needed plus it's easy to use and it's quick .

This is an amazing little device. Connected the battery, it showed the voltage to a tenth of a volt; right on. Plugged-in various MOSFETs, 2-lead diodes, 3-lead diodes (common anode), bipolars, SCRs, and resistors. All of them were identified right-on. The resistors measured within a couple of tenths of what our 4.5-digit Fluke reported ! LEDs showed up as a 2-lead diode. Zeners (under 9V) seemed to work. This tester identified the device no matter how the leads were inserted into the ZIF socket. Now I can sort through those grab-bags of parts I've collected over the years. I'll repost if anything changes or anything new comes up.

I bought the Yosoo primarily to have a back-up for comparing results from other test equipment I have in the lab.So far I've used it for selecting transistors for high hFE (dc Beta) and JFET's for Vgs(f). hFE results are within 10% of my other meters and Vgs was spot on for a number of J-211 VHF JFETs. Resistor and capacitor values are also accurate. I like it's small size and the fact that the display is socketed so I can use a short ribbon jumper to relocate it to the panel on a small cast aluminum enclosure I plan to use for it.. The display contrast seemed fine to me so I didn't attempt to adjust it since some reviews say it's a convoluted process at best.

The Yosoo isn't without its weaknesses. There are many variations of this tester available all based on the ATmega328 microcontroller and they all seem to have different functionality depending on their firmware and hardware implementations. This complicates the job of writing a decent users manual which would have been helpful because zero documentation is included with this tester, not even the usual "thank you for buying from us" note found with most items I buy from our very clever Chinese engineers. Yosoo must assume that buyers are capable of researching what's out there on the web and capable of understanding the ATM328 data sheet. I still think Yosoo should include some minimum documentation.

Since this meter is designed to operate on a 9 V battery, it shuts down after each test to save power which is a royal pain if, as in my case, you plan to build a small regulated analog supply for it. I'd prefer that it have a power switch and stay on as long as I'm using it or have a menu driven auto-off or sleep mode timer. I'm sure I'll eventually figure out how to work around this limitation but it's going to be another time sink in a life that has too many time pressures already. Some minimal documentation from Yosoo could have helped in this case. You might want to find a small plastic or cardboard box the size of the GM328, line the bottom with some ESD safe material and use the meter while it's laying in the box. Without an insulating layer you risk the possibility of shorting the exposed solder connections on the bottom of the board.

The price is low enough that even with the "issues" I've mentioned, the GM328 is worth buying if you want a small foot print component tester with a long list of capabilities. I've only begun to understand this tester and think that over time I'll find many more functions and uses for it.

TI've been looking for a transistor tester for years, and had my eye on a US$300 unit that, alas, was discontinued by the time I got around to ordering it. I took a chance on the Yosoo GM328 based on the customer reviews; it arrived yesterday, and I tried it out last night. Not only did it identify NPN, PNP, and MOSFET transistors -- which was my original requirement -- it also identified capacitors, resistors, thermistors, diodes, and inductors. Further, it identified SCRs and dual-colour LEDs (both those with two leads and those with three). The only things I've tried that it hasn't identified are ceramic resonators, which it sees as capacitors (quite reasonably, considering their internal circuitry), and linear devices like voltage regulators.

Pros:
o Identifies almost every simple component I've thrown at it.
o Excellent value for price.
o Provided with attachment points if you want to put it into a box.
Cons:
o Bare-bones and caseless.
o Contact points on back of PCB are exposed if you set it down on something conductive, possibly leading to damage.

I consider this an excellent bargain, and a treat to use. A little rubber cement and a non-conductive felt backing, and it's got a home on my bench.