Yes and no.
Moisture sensors measure the resistance or conductivity (lack of resistance) between two elektrodes. This value is turned into an output.
This means that for an accurate measurement, the elektrodes need to have some kind of 'water bridge' that connects them. In our inorganic soils, there's usually too much air. The current from one elektrode might not reach the other one because or inorganic pellets aren't touching each other; the current can only pass through water.
Below 60% soil moisture content, it is very well possible that water is present, but not leaking from our substrate enough to form a bridge from one pellet to another, and another, and so on until it hits the second elektrode. The electrical current could take another path through the pot and show an entirely different value due to the resistance that occurs due to the long path.
Regular dirt acts more like a sponge, measurements can stay accurate between 10-100%. With bonsai soils I estimate the accuracy to be somewhere between 60-100%. This'll tell you when you don't have to water, but not exactly when you should water.
However, if you build a sensor yourself (google Arduino DIY moisture sensor, the total kit is less than 40 $ and fun to fiddle around with) then you could log how much water a tree uses during certain weather types, and graph those to make an average.
I made an arduino system that does just that (humidity, soil moisture, temperature, date + time all combined in an excel file). But I never bothered to use the data.
