Geiger counter cannot tell what is the origin source of radiation. Using iMetry, you can identify whether if the radiation origin is from Cesium or radon, so easily. You can identify marble based radiation or reactor origin Cesium, instantly in the field. Without iMetry, you cannot tell 0.15 μSv/h radiation whether if from marble stone radon or cesium. In case of 0.15 - 0.2 μSv/h (it's regular radiation level of natural marble origin), it takes roughly about 30 minutes to tell whether if it is from reactor origin cesium or marble, using iMetry spectrometry mode, without extensive experience.
You may require extensive inspection for final judgement using Germanium spectrometry, iMetry can only be used for initial rough screening, but much better than simple Geiger counters. iMetry require Ba133, and Cs137 calibration source for recalibration.