Bests & Worsts Reviews from Amazon

I'm a science researcher in National Lab. I bought one Corentium Home Radon Detector (Airthings 223) in September 2018 and my friend bought same one in October 2018. We compared these devices' result at the same time in a basement for 3 weeks in November, 2018. Both devices were closed each other: 2 cm distance as shown in the picture. The measured values were supposed to be same value within reasonable tolerance, however, the two devices showed totally different measurement results. One was 1.72 pCi/L and the other was 3.18 pCi/L for long term average. This means that the device's accuracy is very poor or calibration was totally wrong. I'm so disappointed from Airthings and I DO NOT recommend this Radon detector. After contacting manufacturer, I will update their response. Update on 3/9/2019: Customer service was good. They respond immediately and replaced the item by new one. I wanted re-calibrate the item, so I can compare the value before and after calibration. However, they could do only replacement instead of re-calibration. Currently I'm testing new item and will update result soon. Update on 11/14/2020 Sorry for late update. This replaced new Airthing had almost same value with the left-sided item of the uploaded picture at the same location and condition. Recently, radon was measured twice by the replaced new Airthings 223 and Model 1028 of Sun Nuclear co. simultaneously for each 48 hours in my basement. In first measurement, this Airthings 223 had 0.24 pCi/L and the Model 1028 got 0.5 pCi/L with frequently opening window condition. The second measurement with closing windows condition, Airthings had 0.74 pCi/L and the Model 1028 got 1.6 pCi/L. The Model 1028 is calibrated Sun Nuclear Corporation in Florida every year. Then, it looks actual value is around two fold of my new Airthings 223 value. Manufacturer's calibration is totally wrong and they don't serve re-calibration.