not effective at all

I bought this thermometer because I had a mercury that I found too difficult to read water and too imprecise. The shape of it is actually more fun and more effective in theory and this allows reading, but it is very slow (not quickly adjust to the temperature) and the temperature is never accurate (more than one degree often! at first I always checked with another thermometer because the indicated values ​​seemed to me strange).
And when we put the foam in water that's even worse!

I am therefore not satisfied at all!