Having 2 degrees in biochem and molecular biology (BS,MS), I will tell you not to waste your money on any meter under $60-80. The one linked above for $7, I can't believe that is worth anything. The Hanna meter (which I own) is the bargain basement lowest option I would spend my money on.
pH meters are sensitive and non-cheap equipment.
Buy several sets of calibrating solution, re-calibrate every time you use it. Store the electrode wet. Keep a gallon of distilled water around for rinsing.
As for acid testing, one is well advised to invest in a real titration buret and a stand. If you titrate with a syringe, like comes with the kits, it is a rough approximation only.