I used to sell and service the Hanna meters and electrodes.
The "HI98128 pHep®5 pH/Temperature Tester with 0.01 pH resolution" is as good as you can get without buying a discrete pH meter with separate electrode and temperature probes. The Hanna electrodes are some of the best on the market; construction and chemistry are World class.
The HI98128 has a replaceable probe; unplug the old and plug in the new. It also has an extractable cloth junction. This means you can renew/refresh a clogged electrode many times, this is handy if you're reading hopped/oily/high-protein specimens. As a field meter they're hard to beat (for watery type samples). (Don't use these for sewerage or wine.) For homebrew and hydroponics etc they're money very well spent.
Always keep any electrode hydrated. Storage solution will give you years of life on the single electrode. Don't store them in buffer nor in water! If filling the cap of the electrode with storage solution, be very careful not to hydraulically damage the bulb or the junction (it's possible to force solution into the junction and this ruins the chemistry of the 1/2 cell).
Most of the cheap all-in-one meters are clones of the early generation Hanna instruments. Hanna was making their old models for rebadging, but I don't know which badges anymore. The electronics in the clones is usually OK and is often much beter than the chemistry in the electrode, but you need both to make a good reading. Only buy cheap if it's from a long establshed scientific supplier... but, even then, don't expect it to last. The DOA rate on the low-end stuff is high, from all mfgrs/vendors.
If you find a working second hand meter, that has a BNC connector for the pH electrode, it could be a good buy if the elctronics are working fine. Around $80-100 will buy a new electrode that will last years. Be cautious of 2nd hand meters that show any signs of water damage or salting on the case. If you find a working waterproof Hanna meter in a bargain sale, buy it! (They're practically bullet proof.)
Cheers
