Honestly, when you spend $12 on a thermostat/hygrometer you have to know you're not getting the best technology/accuracy out there, right?
They're junk.
I used these things for about three months ten years ago; bought six, set them all up with the probes within an inch of each other in the same room. Got a difference of 12 degrees between them all, returned them all and bought my first (real) thermostat (Helix and the time). Best $120 I spent and it worked like it should.