I use the General Hydro one (well, I splurged on a Milwaukee 'pH testR' last week that a friend sold me for $35 new in box, woo hoo!!! deal of the year!!!) and they work fine. Sure, you don't get more than 0.5 pH points precision, but this is an art, and you don't need to be more precise than that. There is an acceptable RANGE of pH for happy plants, and you will have no trouble finding it with drops.