I have worked with pocket pH probes quite a bit (Sorry for the long reply.) I have not worked with conductivity meters. For pocket instruments, they are usually separate.
You need to decide 1.)How accurate you want this probe to be (temperature compensation on the pH reading? Two digits after the decimal point?) 2.) How much time you are willing to spend in calibration and 3) If size matters. That will define your options. When I was shopping I was looking for a waterproof pocket probe with temperature compensation which could be easily be purchased by several districts, with easy enough instructions that I would not have to personally train every operator. If your requirements are different, your choice of probe will also be different.
Hach doesn't have a pocket pH probe, but does have some larger, higher-end probes. Their products are usually good quality and operator friendly. If they ever do come up with a field probe, I will certainly be looking at it.
The USABluebook catalog has a variety of pocket pH probes and conductivity probes. I have worked with the Oakton pH Testr 2+ (one digit after the decimal, compact, temperature compensated but no temperature reading capability) and the pH Testr 3+ (two digits after the decimal, compact, temperature compensation and temperature reading.) We have had numerous field problems with the pH Testr 3+. They take a long time to calibrate and they have a tricky cleaning regiment that is not described in the instructions (I called the supplier to get the cleaning procedure. I’ll happily share it if you choose that probe.) I suspect a lot of our operator field problems are due to not cleaning the reference junction properly. In comparison, we have had fewer problems with the pH Testr 2+. If you need the extra digit of accuracy, though, you have to go for the more expensive one with the longer calibration time.
I have also worked with some of the Hanna probes. I found that the calibration procedure for the pHep 4 was a bit strange. (The probe has a display that says it should be placed in a pH 4 buffer, but if you put it in the pH 10 buffer it would be okay – I would have gotten way too many field calls if I had chosen that one.) It was also less accurate. It would easily be off by 0.2 pH units right after calibration. The good thing about it was that it used regular batteries not watch batteries.
