It seems to measure very accurately.
I have another plate meter with which it coincides exactly, both in temperature and humidity, so theoretically it is correct.
As for the negatives:
°It is tragically small, I didn't even read the dimensions because I didn't expect it to be so small. (a little smaller than a matchbox)
°It has "large" letters for humidity and small letters for temperature. I would prefer it the other way around.
°It does not have decimals for temperature. 19 will show as 20. There are no intermediate values.
°It takes a small watch-type battery, I would prefer an AAA battery that we all have readily available at home when needed.
As for the positives, besides the accuracy, it also has a satisfactory refresh rate. From the 2 degrees it showed in my fridge to the 19 in the room when I took it out, it took about 5 minutes. Others take 15++.
Its price for a very simple, small hygrometer/thermometer without anything else is somewhat high, but the brand is of good quality.

Extech manufactures hygrometer devices for professionals. And this small (50mm X 40mm) device is of the same quality as their expensive instruments, so it should be the best value out there. It functions well in both small and large areas. Surprisingly, it is easy to read without the need for reading glasses. I just wish it had a backlight for the display. It is as accurate as their larger hygrometers that cost three times or more. I would recommend this hygrometer.