In some ways this hygrometer works fine. It is very sensitive to changes in humidity and the readings are consistent. The display is easy to read, even at a distance.
The problem is that the readings are consistently WRONG. I've compared it with several high quality thermometers/hygrometers and the TFA "Cosy" Thermo-Hygrometer is consistently showing 2 degrees above and close to 10 % air humidity below all the others (the others all show more or less the same).
As long as I'm aware of this I can still use this hygrometer of course. It does seem to be very precise and consistent, just consistently WRONG. It seems to have a calibration issue rather than malfunctioning.
Still, it does not work the way it's supposed to so it will have to be a "poor" rating I'm afraid.