I used moisture meters for several years before realizing I was allowing the seemingly scientific readings to overrule my common sense. Then, I learned that these devices do not really measure water content. They measure electrical conductivity between two different types of metal on the probe. It assumes that water is the only conductor of current and that is not true. Plants in soil that is very dense or high in mineral salts will cause the meter to read higher than it should. Very porous and some sandy potting mixes tend to read very low. If all your plants were in the same potting mix and the mineral content (water quality, fertilizer) was consistent and carefully controlled, then these meters could be reasonably accurate. But that is rarely the case. My advice is to trust your experience and common sense and not be overruled by a pseudo scientific technical device.
I do use an inexpensive plastic soil probe (Soil Sleuth) that does allow me to pull tiny bits of soil from deep within a pot and see just how damp the soil is up to a foot below the surface.
