I bought what I believe is the same unit (~$15 on Amazon) just for curiosity, to see how/if it works. The instructions are quite rudimentary, and I could not get calibration to work, 2-point or 3-point. When reading their buffers on our Vinmetrica SC-300, the pH 4.00 was fine, but in my hands their pH 6.86 buffer measured 6.97, and the pH 9.18 came out 9.02. So I returned it.
So... I bought one of these cheap pH pens just to check it out. I'm not sure if it's the exact model used by pproctorga; there are seemingly a dozen brands on amazon.com that all look alike, I'm sure they all come from the same factory in China. My first day impressions:
- The package came with a pH pen, 3 buffer powders and instruction sheet. There was also an envelope saying 'Please check the warranty card inside'; this had no warranty information but indicated that I could receive a $30 Amazon gift card by contacting them. A little digging around suggests that this is their way of trying to get me to leave a 5-star review on Amazon. Not a great first impression.
- I made up the buffers in 250mL each distilled water as directed. I left the probe in an aliquot of the pH 4.00 buffer for 45 minutes in case the glass bulb needed rehydrating. Nominal pH reading at this stage was ~3.1-3.2, though I wasn't too concerned as I would always calibrate before use in any case.
- I used a wash bottle of distilled water to clean the probe between measurements. The instructions say to wipe the probe clean, though I don't think this is a good idea: you shouldn't touch the glass bulb on a pH probe.
- Calibration involved placing the probe in the standard buffers for a few seconds while stirring gently, then holding the CAL button for 5 seconds. The instrument is supposed to autodetect which buffer you're using. The instructions say that just one buffer (6.86) is sufficient for accuracy of +/- 0.1 pH unit, but to calibrate in all 3 buffers for maximum (+/-0.01) accuracy.
- Calibration in the 6.86 and 4.00 buffers seemed fine, but I could not get it to register the pH 9.18 buffer. Following the 2-point calibration, the value of the third buffer seemed to be around pH 9 - but on pressing the CAL button it would always read 6.86.
- I figured that the 2 lower pH points should be sufficient for testing wine samples, though I don't know how their algorithm works; there are no instructions suggesting that you can use just 2 points. Nevertheless I repeated the calibration with the 6.86 and 4.00 buffers, and tested a sauvignon blanc sample that I had lying around. This measured as 3.60, which seemed reasonable; I knew that this particular wine was on the high pH/low acidity end of the scale.
- Repeat measurements of the buffer solutions gave values of 4.03 and 6.87, which I thought were surprisingly consistent.
- Repeating the wine and 2 buffers again gave values of 3.57, 4.07 and 6.92. Again, not too bad for a $10 instrument but maybe a bit drifty.
I think I've learned enough to conclude that while this isn't a total bust, it's definitely a bit squirrely. I would use this to get quick and dirty pH estimates where I didn't care about the 3rd significant figure, but I will look around for a more robust solution for my winemaking endeavors. All of the other options mentioned in this thread (Milwaukee, Extech, Apera, Hanna) seem like they might fit the bill.