It is my understanding that this meter can measure the entire pH scale; it is designed to be calibrated with a pH 7.0 solution and either a pH 4.0 solution or a pH10.0 solution. However, it is designed for the aquarium market, not as a laboratory instrument, so I wouldn't look to it to measure extremes. I'm using mine in a saltwater tank, where the pH is typically in the low 8's.
This meter should work well for any aquarium situation, but it is intended to be in continuous use, not used as a portable pH meter. The sensor tip should always be kept wet, either in the aquarium or with approved fluid inside the cap.
The manufacturer may be able to more thoroughly address your concerns.