I have the Hanna Instruments HI 98121 pH/ORP/Temperature Tester.
Available on Amazon for $89.
I have used it 3 years so far and no problems.
Still on its original battery.
However,.......
1. I recalibrate it using 2 point calibration solutions every 2-3 months.
2. Without fail I NEVER let the pH glass bulb dry out and always store it with cap on after placing a drop of pH storage solution (potassium based) inside the cap.
3. ORP works fine, but is SLOW....takes 5 minutes to get a reasonable reading. pH is much faster.
4. Temperature is integrated and displayed and used to temperature compensate the measurements.
5. I wipe the bulb off a couple times a year with a paper towel.
6. I rinse the bulb sometimes after use in R.O. water....but sometimes I don't and just replace it back into its storage solution.
So to maintain this meter you need:
1. Two calibration solutions.
2. Storage solutions.
3. Keep the bulb wet and clean.
I have found the meter to be overall reliable. If you let your bulb dry out and are unable to recondition it, then the bulb is replaceable.
The meter is completely water proof. Everytime I use it, I just take the cap off, turn it on and toss it in the pool. I let it float for 5 minutes and take my readings and I am done. Sometimes I let it float in my SPA and watch the ozone run the ORP up
Good luck... Lee