Just so you are clear on what you are getting, you get three thermometer strips (sticky on the rear) and that's all. You do not get anything else to make them into little cards.
I have one on the wall in the nursey and one in each moses baskett on a peice of card. They are pretty accurate and give you a good temperature range.
If all you want is an idea of the room temperature, then buy these. If you want an exact room temperature then spend more money and buy an electronic thermometer. However, why do you need to worry yourself with the exact room temperature. Walk in the room and if its too cold to you, increase the temperature, if its too warm, then decrease the temperature. If the temperature on one of these strips is between 18-21, then you have it just right! Don't let other companies worry you into buying fancy gadgets. All you're doing is spending loyts of money for something that these strips can tell you.!