I bought the thermometer based on the good reviews and the price, and I received it last week within the specified deadlines. So far, so good.
I followed the enclosed instructions and decided to test it in my oven (Miele), which is now ten years old and lately I have not been satisfied with its performance.
I tested it with and without air, allowing enough time for the temperatures to stabilize from 50-250 degrees Celsius in intervals of 25 degrees.
There was a deviation of 10-20 degrees, with the thermometer showing lower temperatures compared to the thermostat setting.
At this point, I initially thought that the oven was to blame, but I considered that the thermometer may not be properly calibrated from the factory, as I noticed that the needle-pointer did not move smoothly during heating but rather with "jumps". I wrapped it in a thin plastic membrane to make it waterproof and tested it in a small amount of boiling water (depth 1.5 cm).
Our house is not so high that it affects the boiling point of water in equilibrium with steam and 1 atmosphere pressure (100 degrees Celsius).
It took quite a while to stabilize at a temperature of 85 degrees and the needle moved with "jumps" instead of smoothly.
Conclusion: The mechanism of this particular thermometer is faulty and the oven works fine.
Therefore, I do not recommend its purchase. Maybe I was unlucky and got a defective device that I think should be replaced, but maybe not.

Readable, stable, accurate. It is perfect for the oven. Great durability. I highly recommend it!!