I have a Kestrel 4000 and I love it, it is a great device and is as accurate as one can expect from a handheld weather meter.

I had heard over the years how inaccurate and finicky handheld weather meters can be, primarily stories of off the wall RH readings. Historically this has been true, especially at lower RH values. However, with the Kestrel I have found that the RH values have always been within 1-2% of values I would get with a sling psychrometer and tables. While at extreme low RH values, a few percent difference can mean a huge difference in fire behavior, I have come to question which is more accurate a hand spun psychrometer and a tired firefighter reading a paper table full of tiny numbers, or a quality weather meter like a Kestrel?

As for calibration, I do calibrate my meter every year in April and after every deployment. It requires a calibration kit and being left for hours in enclosed containers, it is pretty simple to do. Most people only caibrate it once a year if that often... and they remain accurate.

Oh, and they make any other weather meter I have seen on the market (in the same price range and size) look like a toy in comparison.