Product review (3 stars): Not very accurate - It reads 10% lower than my other AcuRite meter.
I bought this meter since it shows 0.1% readings for humidity and that's hard to find.

I knew that feature would be optimistic at this price point since it's claimed accuracy of + - 2% is 20x higher than the lowest unit of the display.  So I expected the last digit may be mostly noise and that is certainly the case.

Sitting on the kitchen table for hours (even in a sealed glass bowl) the display moves up and down on it's own every few minutes.  It will say
50.1%,
50.2
50.3
50.4
50.5
50.3
50.1
49.9
50.1
50.2 etc and gradually move up or down several percent while the conditions were stable.

Meanwhile my AcuRite 01033 meter right next to it showed no change during that time which is correct.
It's quite unusual that it can display 1/10 of 1% at this price point so that's useful (if it was accurate)  but in the end it's mostly noise.

The main useful feature is that it does update fairly quickly with 1 reading every 10 seconds.

Since the sensor is mounted internally it still takes a while to get an actual, relative reading, while meters with an external sensor mounted on the end of a long probe respond quicker to environmental changes.

Meters at this price aren't very accurate for absolute readings but can be used for relative readings if you don't mind it being off 5 -10% as is typical for budget meters.  The claimed spec of +-2% accuracy appears very optimistic based on the readings and drift of the one I received.

The calibration feature is a good idea but the meter needs to be more stable to use it.
At first this one read 10% low, so I pre-loaded it by + 10% to match the other AcuRite meter.  Then later it read too high so I had to back it off the other way.  If a calibration doesn't last 1 day and only calibrates the entire reading regardless of the range that's not that useful.

It needs a 2 point calibration such as at 30% and 80% as High/Low points for that feature to really work.
I realize they can only do so much at $20 but if they made it stable and we could really calibrate it, then it would be quite useful.