I believe its what you spend on the device is what you get if you pay 300 bucks you will have a nice reliable testing device if you pay 15 bucks for it might as well throw it in the trash..
As for my temp gauges with the probes going all the way to the bottom sometimes they read at 71 and a second later 80 degrees but wouldnt see why not.. name and price is the reliable factor in my opinion..
Chemical tests are 99.9% of the time more reliable, or at least more accurate. There's going to be more user error than the gauges but again they will give you better readings.
The gauges in the tank have a life span that is much shorter than chemical tests. I wouldn't bother for pH unless you're expecting swings ( adding CO2, chemical buffers, etc. ).
I guess it was just a wasted $17. I was hopeing this gauge would work so I could put away the test kit permanently. That's what I get for thinking I could do it the lazy way.
The gauge should work fine for you for it's listed life span. Honestly after a few months your tank should be pretty stable and as long as you're doing regular weekly water changes and not adding chemical buffers you don't really need to be concerned with pH. I test when I feel something is not right in the African/ SA tanks. Not very often.