For a long time I have been using Hydrion pH paper with range 1-12 to measure pH and found that OK to within about 0.5 pH unit but to try to get more accurate readings I have been using the cheapest pen type pH meters I could find on ebay (I don't very often need this accuracy).
Type I tried is labelled PH-009, I think it is intended for Fish tanks and ponds, it comes with 2 buffers,4.00 and 6.86 and I made up 5g/L borax as a buffer pH = 9.2.The meter is set to give correct readings with the buffers by turning a little screw with the supplied screwdriver.The readout is digital. The instructions claim accuracy within 0.1 pH with range 0-14. I found the meter calibrates correctly with 2 buffers and measuring the pH of Xtol the claim of accuracy within 0.1 pH is probably true, at least around pH 8.
But I found after two or three months the reading goes haywire without warning and it's time to get another one.This is after washing with distilled water each use as instructed. This happened to me twice, I'm not complaining as it gives a clear indication the thing no longer works.
So my experience is that these meters are OK and cheap but I don't expect them to last very long in photographic solutions, they are probably mainly for fish ponds.
Any observations on pH meters?