yes. use one. and decide to water when it tells you to... which is much better than guessing, going by the surface appearance of the soil, or shoving a large digit down into the soil rather than the thin little probe. the probe is pretty self explanatory. it doesn't hurt to let plants dry out completely... but if you're not worried about mold, etc... then just water light when the meter reads half way between wet and dry.... water heavy when it says dry, and skep watering when its in the upper wet range.
