I used these in my wood stove many moons ago when I had to make my own bread every day.
The thermometers weigh so little I don't understand why they are charging $9 for postage!

Today I use them in my camp ovens and the Jumbo Camp Oven Mate to get a proper temperature for my bread. 

With the hole in the JCOM lid I can hang one on the side wall and (using chiefs CSI torch) see what the temperature is inside without lifting the lid   

I've done enough tests to know that when the JCOM sidewall thermometer reads 150°C the temp in my bedourie is 180°

I highly recommend them to anyone who is new to camp oven cooking - you can hover your hand in the oven and see the temperature at different stages and eventually, with enough practice, you will be able to tell how hot your oven is without having to use the thermometer