I needed a device to help with processing some second-hand/used 26650 LiFePO4 cells as I had a large number (hundreds) taken from various packs.
I looked for a DIY solution and found this one on hackaday, and ordered two! The devices came assembled and ready to go. OpenGreenEnergy was quick to respond to my questions. One piece of guidance with the tester, be sure to use large enough wires to power the board, and to connect to the battery, as it is able to draw up to one full amp from the battery under test! If the wire is too small, there will be a large voltage drop and the measurement will not be accurate. I recommend at least 16 gauge/1.5mm^2 wire.

It is a great board that is very useful for analysing the capacity of LiPo batteries. By choosing the discharge current, you can set the pace of the discharging process.
I am happy with the purchase. Mr. Amit from Green Energy was very helpful with the shipping process and answered my questions swiftly. He also added a nice personal touch by programming a personalized message that shows up when the device is turned on.

This little device is perfect for those of you who salvage 18650 cells and gives you away to group similar cells for projects. Very simple to use and straight forward if you know your electronics basics. I love the welcome message too! I am happy with this purchase, thanks!

Since as most people, after some time I managed to "hoard" quite some rechargeable batteries for various projects and devices, having some programmable capacity tester that could do more than just show you that battery is OK/dead without any real data seemed like a thing to do. I came across this project a while ago and recently got it (delivery was really fast considering that it was shipped from India to EU. Postal expenses were not that high and the device came well packaged. And sure, I had to pay import duty fee and taxes, but hey, was expecting that. And at this point it should be clear, that you can make the product yourself anyway, if you want to save some money.

I ordered the device without the Arduino(clone), so the additional step was to add the Arduino(clone) and program it. With instructions and available Arduino project, this was really easy done via the Arduino IDE (version 2.x works great!). Use of the attached application is simple and it quickly becomes apparent that having a good HW programmable platform gives possibility for doing extra stuff, not just LiPo and such batteries capacity testing. Just to say, that the capacity testing seems to work just fine (as I started to use the device just today, I tested one 18650 battery (non-brand, 2000mAh), and since it was around 90% charged and testing discharged it until it was ~10% full, a measurement of ~1400mAh capacity seems reasonable. Will repeat with fully charged battery and see. I tested with 500mA discharge current and noted that a heatsink of the op amp was slightly warm. Using a fan looks like a good option for discharges at the higher rate.
A note regarding the communication. For some reason (still looking into this), the voltage reference transistor (LM385) was non-functional and I emailed the developer. The response was really fast (couple of hours), even though this was during the holiday. Together we figured that LM385 is non-functional (developer reported that the PCB assembly was QA tested twice and it worked) however developer suggested a programmatic workaround (since I am using lab power supply with stable voltage there is no issue if reference voltage is hard-coded in application instead of being measured via LM385). Well, will replace that LM385 eventually, they are not hard to find and are not expensive. Thumbs up to a developer for a great responsiveness and a functional fix. And for being very kind!

I am thinking of using the platform also for some other stuff, e.g. to detect the charge level, to test other (NiMH) batteries, to add graphing at some point, etc...

It seems that my comment is currently the first and only one (on Tindie). Be aware that you can find many more review on the original project page!
https://www.instructables.com/DIY-Arduino-Battery-Capacity-Tester-V20/